In an attempt to encourage a work and life balance and close its embarrassing gender pay gap, which reaches to 50,6 per cent, Goldman Sachs launched its new benefit scheme for its employees earlier this montha fund of $20,000 (15,400) to cover the costs of extracting or purchasing donated eggs for prospect parents.

This is not the first time a company announces a scheme of that nature. In 2014, tech-titans Apple and Facebook made headlines when they announced that they would include the option of egg freezing among their work benefits. Goldmans Pathways to parenthood project also includes delivering mothers breast milk to their children should they have to be away for work, and offers emergency nannies to look after unwell children.

While the efforts of a company of monstrous power to close gender pay gaps should not be dismissed, the reality is that it wont solve mothers problems and maintain a work and life balance. Rather, it will only increase their time spent at work by preventing women from being there for their families or even being present to in order to create one.

Egg freezing is a method of fertility preservation. Some women wish to freeze their eggs for medical reasons, such as cancer or any other illness that may trigger early menopause (in that case the process of egg freezing can be funded by NHS). Alternatively, other women go for social egg freezing, referring to women who wish to conceive at an older age due to career or high-risk career jobs (such as working in the army) or women who have yet to start hormone therapy when wishing to go through a sex change.

The process overall lasts 12 to 40 days, beginning with the womans circle, explained Suvir Venkataraman, the general manager at Harley Street Fertility Clinic in London. The ovaries are hyperstimulated with hormone injections in order to produce more than a single egg (which is usually produced in one menstrual circle). The eggs are then retrieved with a needle via a low-risk surgical procedure, individually fast-frozen via a method called vitrification, and placed in liquid nitrogen until needed. The eggs can usually be stored for up to ten years.

The treatment costs 3,500 but the medicine can cost from 600 to 1,800 depending on the patient. Overall were issuing a cost of 4,000 to 5,500 per circle, says Venkataraman. On top of the costs, you will need to undergo the procedure to fertilise the eggs (called ICSI) and factor in the potential of more circles needed in order to bank 10 to 20 eggs for a successful outcome, as only a small percentage of eggs are mature and capable of being fertilised. The success rate? In the past, the survival rate of frozen eggs was 30 per cent now its 90 per cent, shares Venkataraman.

Its hard to give a definite answer, however, as only 2,000 babies have been born worldwide from frozen eggs, 700 of them in the UK, according to the Human Fertilisation and Embryology Authority (HFEA). In 2017, only 19 per cent of IVF treatments using the patients own frozen eggs were successful. Furthermore, regardless of the condition of the fertile eggs themselves, older patients are at an increased risk for miscarriages and pregnancy-related complications.

Freezing fresh embryos (either from a donor or the patients partner), on the other hand, has a higher success rate, as embryos are not affected by the length of time they are frozen for. The process has helped prospect parents, and Hannah Selinger was one of the patients who had frozen her eggs, too. Sellinger spent $17,000 and claims that she regretted the whole process. She conceived naturally and, sardonically, during her pregnancy had found out that her eggs were destroyed. The reason was a lapse in communication, as she didnt receive the egg-rent reminders due to her moving to a new place.

Discussing Goldman Sachss scheme, Sellinger said that despite her experience she isnt against egg freezing, and that she believes the problem lies elsewhere. I think the real problem is to care about mothers, make sure that that mothers take six months to a year off, and that should be the case for paternity leave, too. It would be wiser for my government to move into that direction rather than ban abortions, I am only able to have children cause my husband makes enough money from me to do what I do.

While Venkataraman claims, Its really nice that we can help someone, because it means that theyll do as they please. Because we all live longer, our quality of life is better, we are able to stretch our biological clock and egg freezing allows women to do that with fertility as well. Its a great option but I dont think the socio-political system should force someone to do it. If you wish to freeze your eggs, feel free to do it. But dont do it because your company told you to, because your company wont care about youit will care about the money youre making.

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Egg freezing has become standard practice for big companies, but what are the pros and cons? - Screen Shot

25 November 2019

We are currently experiencing powerful digital, artificial intelligence, genomic science, epigenetics and human reproductive revolutions. These will increasingly blur the lines between the physical, digital and biological spheres.

However, as these technological advances create immense responsibilities, new national and international laws, policies and safeguards will become increasingly necessary.

As more people embrace the transformational impact of these technological revolutions and calculate the economic benefits, I predict that we will see new trends resulting in fewer natural conceptions, more genetically planned parenthood and increased demand for fertility treatment. This is good news for the fertility sector.

DNA (genetic) sequencingnow costs a few hundred pounds per genome, making its integration into the mainstream possible. Interpretation costs are additional, but seem likely to fall. It makes increasing economic sense to invest in genomic sequencing and possible remedies at the outset of fertility patient treatment.

Whole genome sequencing can currently help identify upwards of 40006000 diseases and this number is likely to grow. It is far cheaper than the cost of treating a sick child or adult and lost productivity in the workplace. It is likely to decrease the costs of institutionalised care and result in healthier people living better quality lives. This in turn is likely to increase GDP and lead to greater innovation and development of society as a whole.

Genome editing technologies are becoming more accurate, affordable and accessible to researchers, and could in future help switch genes on and off, target and study DNA sequences.

As genomic science and medicine becomes part of mainstream healthcare provision, I predict we will see a shift in perception towards genetically-planned parenthood to have a healthy child. This technology will help alleviate a biological lottery at birth, avoid condemning children and adults to preventable disease, pain and suffering and has the potential to improve opportunities in life. It could also help address fundamental societal issues of declining fertility levels, later-life conceptions and ageing populations.

At ground level, I expect to see changes to delivery of fertility treatment and patient care. The typical fertility patient treatment model is likely to evolve, incorporating three additional genomic steps at the outset: genomic sequencing, genetic counselling and genetic medicine (including genetic screening and genome editing).

Genomic technology, therefore, has great potential in preventing serious and deadly hereditary diseases and over time we will inevitably see greater pressure to push the boundaries of human genetic enhancements.

In the UK, the implantation of a genetically-altered embryo into a woman is currently prohibited under the Human Fertilisation and Embryology Act 1990, (as amended), excepting under certain conditions to prevent the transmission of serious mitochondrialdisease.

Taking account of these rapidly evolving sectors will require centralised state law and integrated policies. We would benefit from a dedicated Ministry for Fertility and Genomics, with a Minister providing a unified voice, agenda and future direction for the fertility sector as a whole. This would help develop a robust genomic and fertility policy and political strategy encompassing pre-conception through to birth and future genetic legacy.

Added to this, we should ensure the integration of specialist legal services to help protect fertility patients (and future born children) undertaking complex treatment and provide a truly multi-disciplinary medico-legal process.

We will also need informed and effective oversight of genomic science and medicine to protect standards and prevent abuse of this technology. Close oversight, accountability and transparency will be required, and regulation must strike a careful balance between respect for the individual and the interests of the state.

Law and policymakers must adopt caution in deploying these powerful technologies, and it will be important to see how countries across the globe meet the challenge. It will be vital to seek international consensus and build new international legal infrastructures to mitigate the risks and prevent rampant genomic and fertility tourism.

It will require engagement and commitment to help law and policymakers build effective legal and regulatory frameworks that will safely and successfully harness the enormous transformational power of genomic science and medicine in the fertility sector over the next 1020 years and beyond.

Success is there for the taking, but the stakes are very high and we overlook root and branch law and policy reform at our peril.

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Why we need root and branch fertility law reform - BioNews

November 25, 2019 (American Thinker) Today, largely due to government policy, doctors' offices have been transformed into a big governmentcontrolled business, and the American Academy of Family Physicians (AAFP), the leading body for family medicine in the United States, appears to prefer it that way. As older doctors like me leave the field, young idealistic physicians bypass family medicine; they are neither interested in working for a business nor motivated by a stifling code of political correctness that fails to recognize the dignity of every human being.

Over 50 years ago, purposeful ignorance of the definition of reproductive health and basic embryology initiated family medicine's decline. Embryology teaches that after an act of sexual intercourse, sperm and egg unite in the woman's fallopian tube, and a human life is created. Seven days later, that human implants in the woman's womb, and nine months later, the mother delivers her child. Ensuring that this process works as natural law intends is reproductive health care, just as ensuring that the heart pumps blood is cardiac health care. For family physicians, however, 1965 brought with it a new discovery about the beginning of life. No longer at fertilization, doctors now declared that human life began with uterine implantation. The new beginning was based not on Nobel Prizewinning medical research, but rather on a desire to cash in on the contraceptive pill, which occasionally prevents a human life from implanting in the womb. It was more lucrative to simply lie about the beginning of human life than to explain to patients the pill's abortifacient potential. Although appearing innocuous, this unscientific declaration demonstrated that family medicine was willing to sacrifice scientific excellence and medical ethics for consumerism. It set a precedent in which select people can claim something to be a medical fact and redefine it as such without any type of scientific analysis. And finally, it began the involvement of medicine in practices purposefully designed to prevent a human organ system from working properly the antithesis of health care.

This deception, led by physicians and amplified by governments, has led the world to believe that the reprophobic practices of contraception, abortion, and sterilization are the main elements of reproductive health care. The absurdity of this belief could best be compared to a government proposal in which physicians would prescribe alcohol as the main component of neurologic health care. Without ever entering into dialogue within the medical community about the pros and cons of enticing people to be more sexually active by unnaturally inhibiting the reproductive system, reprophobics became an essential element of health care. Although lucrative, the negative effects on the family of such treatment, including increased teen sexual activity, infidelity, and the death of family members, should be something family medicine physicians are particularly concerned about. But the AAFP is not, preferring to virtue-signal about the politically correct subject du jour while keeping the "family" in family medicine devoid of any real meaning.

So integral to family medicine has contraception becomethat not to prescribe it makes working as a physician difficult. Unable to afford the bureaucraticexpense of private practice, I have felt required on multiple occasions to proclaim religious beliefs as an excuse for my prescribing practices, while groveling before a prospective employer. In retrospect, this was always a weak argument, as it suggested that if not for myunscientific belief in a supernatural deity, I would prescribe reprophobics day and night. In reality, it is my medical beliefs that determine how I treat my patients; God did not order me to have them. They reflect extensive study of the family and sexuality, based on the natural law and its realistic consequences, which my wife and I do our best to put into practice.

Religious belief is just another term that progressives have cleverly co-opted to devalue convictions that are consistent with orthodox Christian values. Beliefs including that life begins at conception, homosexual "marriage" is wrong, and abortion is murder are dismissed as religious. Beliefs that life begins at some other time, gender is fluid, or abortion is great are not and therefore considered of higher importance.

My medical beliefs have helped to keep my family healthy; I want the same for my patients.

Control of prescription contraceptives makes physicians big-money players in the commercial side of sexual activity. The imperfection of contraception in preventing unwanted pregnanciesgives medicine another opportunity to profit, in this case through abortion procedures. The importance of these procedures in American medicine is clearly illustrated by aMay 2019 joint public statement that condemns state laws limiting abortion, complaining that they "inappropriately interfere with the patient-physician relationship" and "unnecessarily regulate the evidence-based practice of medicine." The underlying but unstated premise of the statement, promulgated by the AAFP and five other large medical associations, is that human lives are of different value, especially unborn family members. For unborn lives of higher value, the mother and child become patients, and it is (as it should be) the physician's responsibility to do his best to ensure a healthy delivery. For those of lesser value, the doctor is directed not only to walk away from the doctor-patient relationship, but, moreover, toenable child extermination.

Despite the public statement's grandiloquent description of family physicians as "informed by their years of medical education, training, experience, and the available evidence,"none of that is considered in the final decision about the value of an unborn family member. It is rather the often flawed analysis of a distraught teenage girl with a SpongeBob level of medical knowledge that leads to the life-or-death decision.

Without ever providing a rationale, AAFP directives strip the family physician of his role as true advocate for every pregnant mother and her child. Unable to defend its position on the basis of medical ethics, generally regarded as medicine's highest standard, the AAFP chooses rather to highlight abortion as evidence-based medicine. Voluminous evidence, most recently from the Planned Parenthood baby parts trafficking case, does at least support this claim, demonstrating the deadly effectiveness of this unethical and disturbing medical procedure. However, rather than interfere with the doctor-patient relationship as these organizations claim, recently passed laws mandate the establishment of such a relationship with a child whom doctors would otherwise have cruelly and unethically chosen to discard.

Since 1973, government has legalized a "religious" belief that unborn family members do not automatically deserve the right to life. At the time and continuing today, rather than stand up for the humanity of the unborn, something in which the physician has honored expertise, the AAFP produces condescending and illogical criticism of those voters who do. American medical organizations have allowed government to establish itself as a permanent intrusive member of the doctor-patient relationship and given credence to those who believe that some American lives have less value than others. Hidden behind terms like "reproductive health care," "evidence-based medicine," and "intrusion into the patient-doctor relationship" is our willingness as an organization to sacrifice human life for financial and political gain. When professions whose reputations are established based on Christlike ideals of helping the weakest among us attempt to prosper at the cost of the weak, failure is inevitable except, of course, for those with lives of higher value.

Published with permission from the American Thinker.

Link:
How redefining medicine has redefined the family - Lifesite

Embryology, the study of the formation and development of an embryo and fetus. Before widespread use of the microscope and the advent of cellular biology in the 19th century, embryology was based on descriptive and comparative studies. From the time of the Greek philosopher Aristotle it was debated whether the embryo was a preformed, miniature individual (a homunculus) or an undifferentiated form that gradually became specialized. Supporters of the latter theory included Aristotle; the English physician William Harvey, who labeled the theory epigenesis; the German physician Caspar Friedrick Wolff; and the Prussian-Estonian scientist Karl Ernst, Ritter von Baer, who proved epigenesis with his discovery of the mammalian ovum (egg) in 1827. Other pioneers were the French scientists Pierre Belon and Marie-Franois-Xavier Bichat.

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animal development: Embryo formation

Since the goal of development is the production of a multicellular organism, many cells must be produced from the single-celled zygote.

Baer, who helped popularize Christian Heinrich Panders 1817 discovery of primary germ layers, laid the foundations of modern comparative embryology in his landmark two-volume work ber Entwickelungsgeschichte der Thiere (182837; On the Development of Animals). Another formative publication was A Treatise on Comparative Embryology (188091) by the British zoologist Frances Maitland Balfour. Further research on embryonic development was conducted by the German anatomists Martin H. Rathke and Wilhelm Roux and also by the American scientist Thomas Hunt Morgan. Roux, noted for his pioneering studies on frog eggs (beginning in 1885), became the founder of experimental embryology. The principle of embryonic induction was studied by the German embryologists Hans Adolf Eduard Driesch, who furthered Rouxs research on frog eggs in the 1890s, and Hans Spemann, who was awarded a Nobel Prize in 1935. Ross G. Harrison was an American biologist noted for his work on tissue culture.

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Embryology | Britannica

London - The first "designer baby" conceived using a controversial screening technique is expected to be born next year.

An embryo has been implanted into a surrogate using IVF by US firm Genomic Prediction.

Nathan Treff, chief scientific officer at the New Jersey firm, told the Mail "there is now a pregnancy confirmed" and it is hoped the baby will be born in 2020.

It is understood the parents are a male couple in the US, who are having the baby using a surrogate mother.

The embryo has been selected through genetic sequencing to have a reduced risk of 11 diseases, including several types of cancer and diabetes. While such a test would be illegal in the UK, Genomic Prediction said it intends to apply for a licence with the watchdog Human Fertilisation and Embryology Authority.

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World's first 'designer baby' to be born in a year - IOL

By Pip Murrison & Natasha Mosheim

Profile speaks to President of Students for Life Durham Jolle Lucas about her newly ratified society and the pro-life movement in Durham. An interview with President of Durham Students for Abortion Access can be found here.

Why are you pro-life?

I grew up in a Christian home. It is kind of assumed in that tradition that you are pro-life because we believe that humans are incredibly valuable, that life is a gift from God. But when I was in high school one of my friends asked me the hard question. She said, Well what would you do if a girl was raped or something? And I hadnt thought about that. I went home and I asked my mum that question. My mum just started crying and she looked at me and said well obviously thats horrendous and thats awful, but we dont kill children for the sins of their fathers. We are actually fighting for two victims, we are fighting for a woman and her baby, who were both hurt by someone who was abusive. I think because I heard that emotional, kind response, I became pro-life, it helped cement that.

Do you think that abortion will be abolished worldwide in our lifetime?

I hope that it will be abolished in our lifetime. I would really like to see women given more options, and the abortion numbers to decrease. When abortion was passed in both the UK and the US, especially in the US, the tagline was safe, legal and rare right. Well over 200,000 abortions in the UK is not rare, especially when upwards of 90% of those abortions are not because of health of the mother, they are not because of rape, because of a deadly problem or the foetus or anything like that, they are simply because of inconvenience.

Is abortion unacceptable in cases of rape?

I believe in embryology that life starts at conception. I believe that every human deserves human rights that includes the child. The woman who was raped, her body was violated by the rapist. When you choose abortion, you are also violating the life of the unborn child right, its a similar kind of crime just in a different way, I think that both are wrong. That doesnt mean that I dont have compassion, I think that rapists should be put behind bars at the very least. But I dont think that having an abortion would fix rape. I have done studies on post-abortion counselling and things like that, and its so important and vital that we understand how many women are suffering from post-abortion trauma. If a woman in a normal situation chooses to have an abortion and she suffers from post-abortion trauma, then you go to the woman who is already suffering from the trauma of rape and then add post-abortion trauma on top of that. Why would we want to add to the problem? I was violated, then I tried to get rid of the problem, so I violated and ended up killing another person. I just dont see abortion even in cases of rape as consistent or ultimately really caring, and nothing is going to undo it. We have to find the way thats going to create the least amount of trauma.

Is it ever okay to have an abortion? Even if mothers life at stake?

Pro-Lifers want to save as many lives as possible, hopefully mother and child but if it is a situation where we have to do something as if you do nothing the woman and the child will die, in that case we chose the operation that will save the most lives.

Many would argue that the right to choose abortion is a human right, how would you respond to that?

Some would argue its their human right. I would think that its not consistent and not correct because then youre disregarding the human right of the child. The child inside your body is not your body. Thats a separate human. No woman has two heads or two hearts. Its a separate body. And no person should be able to decide who is valuable and not. These children are just as valuable. But the only difference is somebody decided that they were valuable or not. I think we get into really really sticky territory as humans, when we start deciding that because someone is smaller than us, less capable than us, less able than us, maybe looks a little different than us, that we have the right to decide that they are not human. Because thats how we get the holocaust, thats how we get slavery, thats how we get things like racism and ableism and whatever else you want to call it. If we say that every person is valuable, then we have to include the unborn in that.

Donald Trump says he is Pro-Life but with caveats i.e. abortion is acceptable in cases of rape and incest. Obviously, you dont agree with the caveats, but do you support Trump, based on his Pro-Life stance?

Ive been really surprised with how pro-life President Trump has been, because I was concerned, and thought maybe hes just saying that to get the Republican vote, who knows. Im not one of those people that will say we have to agree on every single point in order for you to get my vote but Pro-Life was the main one and I think anything we can do to protect women and reduce abortion I think is a good thing.

Why do pro-life activists struggle to make their voices heard over the pro-choice campaign?

I think it is because its swept in with other things in Conservatism. Not because Im ashamed, but because I would be scared. Oftentimes there is that silent majority where you have one small group of people yelling really really loudly and everyone else is like I have my voice but I dont need to shout. That can be the case with people that are pro-life. If you say you are pro-life in the wrong crowd, youll get hate, youll get bullied, people will make fun of you and they will make assumptions about you and before you even have a chance to say anything about I care for women or that I spend a lot of time wanting to champion for women and things like that, theyll say you racist, bigoted, women hater, anti-feminist, Nazi. And youre just like, well youve already decided who I am, what more is there to say? So I think that that causes a lot of people to want to be silent.

You talk a lot about how being pro-life for you is tied up with female empowerment. Would you describe yourself as a feminist?

I generally dont use the term feminist because of what the feminist lobby stands for today, I dont agree with them on a lot of things. I dont agree with third wave feminism. I would agree with first and probably second wave feminism. Actually the first feminists were all pro-life. They were huge champions for women. A lot of what feminism is doing today is really just trying to turn women into men. I just dont understand that. What the original feminists were trying to do were to say we can be women, we can love being women and have jobs and vote and we dont have to become men to do that. That, to me, is what being feminist is and what I would like feminism to return to. To say we dont have to be men to be valuable people.

Do you think that the scare factor of having an unplanned pregnancy whilst at university drives students towards abortion? How would you advise someone who has an unplanned pregnancy?

I would say absolutely. Not every woman is the same, for some women it would not matter what the options were, they would just want the abortion. But for the majority of women I have spoken to, when I have said if were to get rid of everything that would be impeding you having this baby, be it funds or a house or a jobs or a boyfriend or whatever, they most often would say yes I would want this baby. I see a massive problem there, that if they had the support they would want their baby and our response is too bad, we will just give you an abortion any way. So I would encourage them to think 10, 30, 40 years down the road, and you look back and can say I made the right choice, the best and most loving choice for me and for this baby. I think all to often we think abortion is the undo button. What we dont talk about is how emotionally difficult it is to end the life of a child, to live with that, we live in a culture that tells women if you chose an abortion you should not feel bad about it, you should feel empowered and you should get over it.

Disclaimer: All views and research cited above are those of the interviewee and are not necessarily reflective of Palatinate.

Image by Jolle Lucas

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I believe that life starts at conception - Palatinate

Introduction

Key Events of Human Development during the first week (week 1) following fertilization or clinical gestational age GA week 3, based upon the last menstrual period.

The first week of human development begins with fertilization of the egg by sperm forming the first cell, the zygote. Cell division leads to a ball of cells, the morula. Further cell division and the formation of a cavity in the ball of cells forms the blastocyst. These notes also cover events before fertilization formation of both the egg and sperm, gametogenesis.

Initially, there is a halving of chromosomal content in the gametes (spermatozoa and oocyte) by the process called gametogenesis. Chromosomal content is then restored by fertilization, allowing genetic recombination to occur. This is then followed by a series of cell divisions without cytoplasmic growth. During this first week the egg, then zygote, morula then the blastula is moving along the uterine horn into the uterus for implantation in the uterine wall.

Implantation also begins in this first week, but will be covered in Week 2 notes, as the implantation process is completed by the end of the second week.

Human blastocyst week 1 movies, 3 above movies together in single table.

Movie - Pronuclear Fusion | Movie - Parental Genomes

Conceptus - term refers to all material derived from this fertilized zygote and includes both the embryo and the non-embryonic tissues (placenta, fetal membranes).

Within the early zygote, at the 2 pronuclei stage, the male pronucleus is "reprogrammed" by the demethylation of the paternal genome. Image sequence shows the mouse zygote at pronuclear stages[2], where the male pronucleus initially contains methylcytosine (5mC, red) oxidises to form hydroxymethylcytosine (5hmC, green).

5mC - 5-methylcytosine (red). 5hmC - 5-hydroxymethylcytosine (green) formed by enzymatic oxidation of 5mC.

Mouse zygote mitosis[2]

Cleavage of the zygote forms 2 blastomeres and is cleavage with no cytoplasm synthesis.

Cell division within these cells is initially synchronous (at the same time), then becomes asynchronously (at different times).

Carnegie stage 2

Carnegie stage 3

Two forms of cellular junctions Figure 21-69. The blastula

Blastocyst Hatching - zona pellucida lost, ZP has sperm entry site, and entire ZP broken down by uterine secretions and possibly blastula secretions. Uterine Glands - secretions required for blastocyst motility and nutrition

There are several important changes that occur in this new diploid cell beginning the very first mitotic cell divisions and expressing a new genome.

The oocyte arrested in meiosis is initially quiescent in terms of gene expression, and many other animal models of development have shown maternal RNAs and proteins to be important for early functions.

The new zygote gene expression is about cycles of mitosis and maintaining the toptipotency of the stem cell offspring cells.

The morula gene expression supports the formation of two populations of cells the trophoblast (trophectoderm) and embryoblast (inner cell mass), each having different roles in development, while maintaining the toptipotency of these populations.

Current research is now also pointing to non-genetic mechanisms or epigenetics as an additional mechanism in play in these processes.

The following figure is from a recent study[4] using video and genetic analysis of in vitro human development during week 1 following fertilization.

A recent paper has measured telomere length in human oocyte (GV, germinal vesicle), morula and blastocyst and found changes in this length in preimplantation embryos.[5] Telomeres are the regions found at the ends of each chromosome and involved in cellular ageing and the capacity for division. The regions consist of repeated sequences protecting the ends of chromosomes and harbour DNA repair proteins. In the absence of the enzyme telomerase, these regions shorten during each cell division and becoming critically short, cell senescence occurs.

See Week 1 - Abnormalities

Dizygotic twins (fraternal, non-identical) arise from separate fertilization events involving two separate oocyte (egg, ova) and spermatozoa (sperm).

Monozygotic twins (identical) produced from a single fertilization event (one fertilised egg and a single spermatazoa, form a single zygote), these twins therefore share the same genetic makeup. Occurs in approximately 3-5 per 1000 pregnancies, more commonly with aged mothers. The later the twinning event, the less common are initially separate placental membranes and finally resulting in conjoined twins.

Table based upon: Twinning. Hall JG. [6]

Embryo Week: Week 1 | Week 2 | Week 3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8 | Week 9

Cite this page: Hill, M.A. (2019, October 20) Embryology Week 1. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Week_1

Link:
Week 1 - Embryology

Embryology around the world (use the translate link by clicking Expand at the top of each page to change to your language) - embryologie (German, French, Dutch, Czech), embriologa (Spanish, Italian, Portuguese), embryologi (Norwegian), embryologia (Finnish), embryoleg (Welsh), embriologi (Indonesian), embrayolohiya (Filipino), (Greek), (Russian), (Japanese), (Chinese), (Korean), (Hebrew), (Arabic), (Persian), (Tamil), (Marathi), (Thai)

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Embryology

This article is about Human embryonic development. For Embryonic development in general, see Embryonic development.

Human embryonic development, or human embryogenesis, refers to the development and formation of the human embryo. It is characterised by the process of cell division and cellular differentiation of the embryo that occurs during the early stages of development. In biological terms, the development of the human body entails growth from a one-celled zygote to an adult human being. Fertilisation occurs when the sperm cell successfully enters and fuses with an egg cell (ovum). The genetic material of the sperm and egg then combine to form a single cell called a zygote and the germinal stage of development commences.[1] Embryonic development in the human, covers the first eight weeks of development; at the beginning of the ninth week the embryo is termed a fetus.Human embryology is the study of this development during the first eight weeks after fertilisation. The normal period of gestation (pregnancy) is nine months or 38 weeks.

The germinal stage refers to the time from fertilization through the development of the early embryo until implantation is completed in the uterus. The germinal stage takes around 10 days.[2] During this stage, the zygote begins to divide, in a process called cleavage. A blastocyst is then formed and implanted in the uterus. Embryogenesis continues with the next stage of gastrulation, when the three germ layers of the embryo form in a process called histogenesis, and the processes of neurulation and organogenesis follow.

In comparison to the embryo, the fetus has more recognizable external features and a more complete set of developing organs. The entire process of embryogenesis involves coordinated spatial and temporal changes in gene expression, cell growth and cellular differentiation. A nearly identical process occurs in other species, especially among chordates.

Fertilization takes place when the spermatozoon has successfully entered the ovum and the two sets of genetic material carried by the gametes fuse together, resulting in the zygote (a single diploid cell). This usually takes place in the ampulla of one of the fallopian tubes. The zygote contains the combined genetic material carried by both the male and female gametes which consists of the 23 chromosomes from the nucleus of the ovum and the 23 chromosomes from the nucleus of the sperm. The 46 chromosomes undergo changes prior to the mitotic division which leads to the formation of the embryo having two cells.

Successful fertilization is enabled by three processes, which also act as controls to ensure species-specificity. The first is that of chemotaxis which directs the movement of the sperm towards the ovum. Secondly there is an adhesive compatibility between the sperm and the egg. With the sperm adhered to the ovum, the third process of acrosomal reaction takes place; the front part of the spermatozoan head is capped by an acrosome which contains digestive enzymes to break down the zona pellucida and allow its entry.[3] The entry of the sperm causes calcium to be released which blocks entry to other sperm cells. A parallel reaction takes place in the ovum called the zona reaction. This sees the release of cortical granules that release enzymes which digest sperm receptor proteins, thus preventing polyspermy. The granules also fuse with the plasma membrane and modify the zona pellucida in such a way as to prevent further sperm entry.

The beginning of the cleavage process is marked when the zygote divides through mitosis into two cells. This mitosis continues and the first two cells divide into four cells, then into eight cells and so on. Each division takes from 12 to 24 hours. The zygote is large compared to any other cell and undergoes cleavage without any overall increase in size. This means that with each successive subdivision, the ratio of nuclear to cytoplasmic material increases.[4] Initially the dividing cells, called blastomeres (blastos Greek for sprout), are undifferentiated and aggregated into a sphere enclosed within the membrane of glycoproteins (termed the zona pellucida) of the ovum. When eight blastomeres have formed they begin to develop gap junctions, enabling them to develop in an integrated way and co-ordinate their response to physiological signals and environmental cues.[5]

When the cells number around sixteen the solid sphere of cells within the zona pellucida is referred to as a morula[6] At this stage the cells start to bind firmly together in a process called compaction, and cleavage continues as cellular differentiation.

Cleavage itself is the first stage in blastulation, the process of forming the blastocyst. Cells differentiate into an outer layer of cells (collectively called the trophoblast) and an inner cell mass. With further compaction the individual outer blastomeres, the trophoblasts, become indistinguishable. They are still enclosed within the zona pellucida. This compaction serves to make the structure watertight, containing the fluid that the cells will later secrete. The inner mass of cells differentiate to become embryoblasts and polarise at one end. They close together and form gap junctions, which facilitate cellular communication. This polarisation leaves a cavity, the blastocoel, creating a structure that is now termed the blastocyst. (In animals other than mammals, this is called the blastula.) The trophoblasts secrete fluid into the blastocoel. The resulting increase in size of the blastocyst causes it to hatch through the zona pellucida, which then disintegrates.[7][4]

The inner cell mass will give rise to the pre-embryo,[8] the amnion, yolk sac and allantois, while the fetal part of the placenta will form from the outer trophoblast layer. The embryo plus its membranes is called the conceptus, and by this stage the conceptus has reached the uterus. The zona pellucida ultimately disappears completely, and the now exposed cells of the trophoblast allow the blastocyst to attach itself to the endometrium, where it will implant.The formation of the hypoblast and epiblast, which are the two main layers of the bilaminar germ disc, occurs at the beginning of the second week.[9] Either the embryoblast or the trophoblast will turn into two sub-layers.[10] The inner cells will turn into the hypoblast layer, which will surround the other layer, called the epiblast, and these layers will form the embryonic disc that will develop into the embryo.[9][10] The trophoblast will also develop two sub-layers: the cytotrophoblast, which is in front of the syncytiotrophoblast, which in turn lies within the endometrium.[9] Next, another layer called the exocoelomic membrane or Heusers membrane will appear and surround the cytotrophoblast, as well as the primitive yolk sac.[10] The syncytiotrophoblast will grow and will enter a phase called lacunar stage, in which some vacuoles will appear and be filled by blood in the following days.[9][10] The development of the yolk sac starts with the hypoblastic flat cells that form the exocoelomic membrane, which will coat the inner part of the cytotrophoblast to form the primitive yolk sac. An erosion of the endothelial lining of the maternal capillaries by the syncytiotrophoblastic cells of the sinusoids will form where the blood will begin to penetrate and flow through the trophoblast to give rise to the uteroplacental circulation.[11][12] Subsequently new cells derived from yolk sac will be established between trophoblast and exocelomic membrane and will give rise to extra-embryonic mesoderm, which will form the chorionic cavity.[10]

At the end of the second week of development, some cells of the trophoblast penetrate and form rounded columns into the syncytiotrophoblast. These columns are known as primary villi. At the same time, other migrating cells form into the exocelomic cavity a new cavity named the secondary or definitive yolk sac, smaller than the primitive yolk sac.[10][11]

After ovulation, the endometrial lining becomes transformed into a secretory lining in preparation of accepting the embryo. It becomes thickened, with its secretory glands becoming elongated, and is increasingly vascular. This lining of the uterine cavity (or womb) is now known as the decidua, and it produces a great number of large decidual cells in its increased interglandular tissue. The blastomeres in the blastocyst are arranged into an outer layer called Trophoblast.The trophoblast then differentiates into an inner layer, the cytotrophoblast, and an outer layer, the syncytiotrophoblast. The cytotrophoblast contains cuboidal epithelial cells and is the source of dividing cells, and the syncytiotrophoblast is a syncytial layer without cell boundaries.

The syncytiotrophoblast implants the blastocyst in the decidual epithelium by projections of chorionic villi, forming the embryonic part of the placenta. The placenta develops once the blastocyst is implanted, connecting the embryo to the uterine wall. The decidua here is termed the decidua basalis; it lies between the blastocyst and the myometrium and forms the maternal part of the placenta. The implantation is assisted by hydrolytic enzymes that erode the epithelium. The syncytiotrophoblast also produces human chorionic gonadotropin, a hormone that stimulates the release of progesterone from the corpus luteum. Progesterone enriches the uterus with a thick lining of blood vessels and capillaries so that it can oxygenate and sustain the developing embryo. The uterus liberates sugar from stored glycogen from its cells to nourish the embryo.[13] The villi begin to branch and contain blood vessels of the embryo. Other villi, called terminal or free villi, exchange nutrients. The embryo is joined to the trophoblastic shell by a narrow connecting stalk that develops into the umbilical cord to attach the placenta to the embryo.[10][14]Arteries in the decidua are remodelled to increase the maternal blood flow into the intervillous spaces of the placenta, allowing gas exchange and the transfer of nutrients to the embryo. Waste products from the embryo will diffuse across the placenta.

As the syncytiotrophoblast starts to penetrate the uterine wall, the inner cell mass (embryoblast) also develops. The inner cell mass is the source of embryonic stem cells, which are pluripotent and can develop into any one of the three germ layer cells, and which have the potency to give rise to all the tissues and organs.

The embryoblast forms an embryonic disc, which is a bilaminar disc of two layers, an upper layer called the epiblast (primitive ectoderm) and a lower layer called the hypoblast (primitive endoderm). The disc is stretched between what will become the amniotic cavity and the yolk sac. The epiblast is adjacent to the trophoblast and made of columnar cells; the hypoblast is closest to the blastocyst cavity and made of cuboidal cells. The epiblast migrates away from the trophoblast downwards, forming the amniotic cavity, the lining of which is formed from amnioblasts developed from the epiblast. The hypoblast is pushed down and forms the yolk sac (exocoelomic cavity) lining. Some hypoblast cells migrate along the inner cytotrophoblast lining of the blastocoel, secreting an extracellular matrix along the way. These hypoblast cells and extracellular matrix are called Heuser's membrane (or the exocoelomic membrane), and they cover the blastocoel to form the yolk sac (or exocoelomic cavity). Cells of the hypoblast migrate along the outer edges of this reticulum and form the extraembryonic mesoderm; this disrupts the extraembryonic reticulum. Soon pockets form in the reticulum, which ultimately coalesce to form the chorionic cavity or extraembryonic coelom.

The primitive streak, a linear band of cells formed by the migrating epiblast, appears, and this marks the beginning of gastrulation, which takes place around the seventeenth day (week 3) after fertilisation. The process of gastrulation reorganises the two-layer embryo into a three-layer embryo, and also gives the embryo its specific head-to-tail, and front-to-back orientation, by way of the primitive streak which establishes bilateral symmetry. A primitive node (or primitive knot) forms in front of the primitive streak which is the organiser of neurulation. A primitive pit forms as a depression in the centre of the primitive node which connects to the notochord which lies directly underneath. The node has arisen from epiblasts of the amniotic cavity floor, and it is this node that induces the formation of the neural plate which serves as the basis for the nervous system. The neural plate will form opposite the primitive streak from ectodermal tissue which thickens and flattens into the neural plate. The epiblast in that region moves down into the streak at the location of the primitive pit where the process called ingression, which leads to the formation of the mesoderm takes place. This ingression sees the cells from the epiblast move into the primitive streak in an epithelial-mesenchymal transition; epithelial cells become mesenchymal stem cells, multipotent stromal cells that can differentiate into various cell types. The hypoblast is pushed out of the way and goes on to form the amnion. The epiblast keeps moving and forms a second layer, the mesoderm. The epiblast has now differentiated into the three germ layers of the embryo, so that the bilaminar disc is now a trilaminar disc, the gastrula.

The three germ layers are the ectoderm, mesoderm and endoderm, and are formed as three overlapping flat discs. It is from these three layers that all the structures and organs of the body will be derived through the processes of somitogenesis, histogenesis and organogenesis.[15] The embryonic endoderm is formed by invagination of epiblastic cells that migrate to the hypoblast, while the mesoderm is formed by the cells that develop between the epiblast and endoderm. In general, all germ layers will derive from the epiblast.[10][14] The upper layer of ectoderm will give rise to the outermost layer of skin, central and peripheral nervous systems, eyes, inner ear, and many connective tissues.[16] The middle layer of mesoderm will give rise to the heart and the beginning of the circulatory system as well as the bones, muscles and kidneys. The inner layer of endoderm will serve as the starting point for the development of the lungs, intestine, thyroid, pancreas and bladder.

Following ingression, a blastopore develops where the cells have ingressed, in one side of the embryo and it deepens to become the archenteron, the first formative stage of the gut. As in all deuterostomes, the blastopore becomes the anus whilst the gut tunnels through the embryo to the other side where the opening becomes the mouth. With a functioning digestive tube, gastrulation is now completed and the next stage of neurulation can begin.

Following gastrulation, the ectoderm gives rise to epithelial and neural tissue, and the gastrula is now referred to as the neurula. The neural plate that has formed as a thickened plate from the ectoderm, continues to broaden and its ends start to fold upwards as neural folds. Neurulation refers to this folding process whereby the neural plate is transformed into the neural tube, and this takes place during the fourth week. They fold, along a shallow neural groove which has formed as a dividing median line in the neural plate. This deepens as the folds continue to gain height, when they will meet and close together at the neural crest. The cells that migrate through the most cranial part of the primitive line form the paraxial mesoderm, which will give rise to the somitomeres that in the process of somitogenesis will differentiate into somites that will form the sclerotome, the syndetome,[17] themyotome and the dermatome to form cartilage and bone, tendons, dermis (skin), and muscle. The intermediate mesoderm gives rise to the urogenital tract and consists of cells that migrate from the middle region of the primitive line. Other cells migrate through the caudal part of the primitive line and form the lateral mesoderm, and those cells migrating by the most caudal part contribute to the extraembryonic mesoderm.[10][14]

The embryonic disc begins flat and round, but eventually elongates to have a wider cephalic part and narrow-shaped caudal end.[9] At the beginning, the primitive line extends in cephalic direction and 18 days after fertilization returns caudally until it disappears. In the cephalic portion, the germ layer shows specific differentiation at the beginning of the 4th week, while in the caudal portion it occurs at the end of the 4th week.[10] Cranial and caudal neuropores become progressively smaller until they close completely (by day 26) forming the neural tube.[18]

Organogenesis is the development of the organs that begins during the third to eighth week, and continues until birth. Sometimes full development, as in the lungs, continues after birth. Different organs take part in the development of the many organ systems of the body.

Haematopoietic stem cells that give rise to all the blood cells develop from the mesoderm. The development of blood formation takes place in clusters of blood cells, known as blood islands, in the yolk sac. Blood islands develop outside the embryo, on the umbilical vesicle, allantois, connecting stalk, and chorion, from mesodermal hemangioblasts.

In the centre of a blood island, hemangioblasts form the haematopoietic stem cells that are the precursor to all types of blood cell. In the periphery of a blood island the hemangioblasts differentiate into angioblasts the precursors to the blood vessels.[19]

The heart is the first functional organ to develop and starts to beat and pump blood at around 21 or 22 days.[20] Cardiac myoblasts and blood islands in the splanchnopleuric mesenchyme on each side of the neural plate, give rise to the cardiogenic region.[10]:165This is a horseshoe-shaped area near to the head of the embryo. By day 19, following cell signalling, two strands begin to form as tubes in this region, as a lumen develops within them. These two endocardial tubes grow and by day 21 have migrated towards each other and fused to form a single primitive heart tube, the tubular heart. This is enabled by the folding of the embryo which pushes the tubes into the thoracic cavity.[21]

Also at the same time that the endocardial tubes are forming, vasculogenesis (the development of the circulatory system) has begun. This starts on day 18 with cells in the splanchnopleuric mesoderm differentiating into angioblasts that develop into flattened endothelial cells. These join to form small vesicles called angiocysts which join up to form long vessels called angioblastic cords. These cords develop into a pervasive network of plexuses in the formation of the vascular network. This network grows by the additional budding and sprouting of new vessels in the process of angiogenesis.[21] Following vasculogenesis and the development of an early vasculature, a stage of vascular remodelling takes place.

The tubular heart quickly forms five distinct regions. From head to tail, these are the infundibulum, bulbus cordis, primitive ventricle, primitive atrium, and the sinus venosus. Initially, all venous blood flows into the sinus venosus, and is propelled from tail to head to the truncus arteriosus. This will divide to form the aorta and pulmonary artery; the bulbus cordis will develop into the right (primitive) ventricle; the primitive ventricle will form the left ventricle; the primitive atrium will become the front parts of the left and right atria and their appendages, and the sinus venosus will develop into the posterior part of the right atrium, the sinoatrial node and the coronary sinus.[20]

Cardiac looping begins to shape the heart as one of the processes of morphogenesis, and this completes by the end of the fourth week. Programmed cell death in the process of apoptosis is involved in this stage, taking place at the joining surfaces enabling fusion to take place.[21]In the middle of the fourth week, the sinus venosus receives blood from the three major veins: the vitelline, the umbilical and the common cardinal veins.

During the first two months of development, the interatrial septum begins to form. This septum divides the primitive atrium into a right and a left atrium. Firstly it starts as a crescent-shaped piece of tissue which grows downwards as the septum primum. The crescent shape prevents the complete closure of the atria allowing blood to be shunted from the right to the left atrium through the opening known as the ostium primum. This closes with further development of the system but before it does, a second opening (the ostium secundum) begins to form in the upper atrium enabling the continued shunting of blood.[21]

A second septum (the septum secundum) begins to form to the right of the septum primum. This also leaves a small opening, the foramen ovale which is continuous with the previous opening of the ostium secundum. The septum primum is reduced to a small flap that acts as the valve of the foramen ovale and this remains until its closure at birth. Between the ventriclesthe septum inferius also forms which develops into the muscular interventricular septum.[21]

The digestive system starts to develop from the third week and by the twelfth week, the organs have correctly positioned themselves.

The respiratory system develops from the lung bud, which appears in the ventral wall of the foregut about four weeks into development. The lung bud forms the trachea and two lateral growths known as the bronchial buds, which enlarge at the beginning of the fifth week to form the left and right main bronchi. These bronchi in turn form secondary (lobar) bronchi; three on the right and two on the left (reflecting the number of lung lobes). Tertiary bronchi form from secondary bronchi.

While the internal lining of the larynx originates from the lung bud, its cartilages and muscles originate from the fourth and sixth pharyngeal arches.[22]

Three different kidney systems form in the developing embryo: the pronephros, the mesonephros and the metanephros. Only the metanephros develops into the permanent kidney. All three are derived from the intermediate mesoderm.

The pronephros derives from the intermediate mesoderm in the cervical region. It is not functional and degenerates before the end of the fourth week.

The mesonephros derives from intermediate mesoderm in the upper thoracic to upper lumbar segments. Excretory tubules are formed and enter the mesonephric duct, which ends in the cloaca. The mesonephric duct atrophies in females, but participate in development of the reproductive system in males.

The metanephros appears in the fifth week of development. An outgrowth of the mesonephric duct, the ureteric bud, penetrates metanephric tissue to form the primitive renal pelvis, renal calyces and renal pyramids. The ureter is also formed.

Between the fourth and seventh weeks of development, the urorectal septum divides the cloaca into the urogenital sinus and the anal canal. The upper part of the urogenital sinus forms the bladder, while the lower part forms the urethra.[22]

The superficial layer of the skin, the epidermis, is derived from the ectoderm. The deeper layer, the dermis, is derived from mesenchyme.

The formation of the epidermis begins in the second month of development and it acquires its definitive arrangement at the end of the fourth month. The ectoderm divides to form a flat layer of cells on the surface known as the periderm. Further division forms the individual layers of the epidermis.

The mesenchyme that will form the dermis is derived from three sources:

Late in the fourth week, the superior part of the neural tube bends ventrally as the cephalic flexure at the level of the future midbrainthe mesencephalon. Above the mesencephalon is the prosencephalon (future forebrain) and beneath it is the rhombencephalon (future hindbrain).

Cranial neural crest cells migrate to the pharyngeal arches as neural stem cells, where they develop in the process of neurogenesis into neurons.

The optical vesicle (which eventually becomes the optic nerve, retina and iris) forms at the basal plate of the prosencephalon. The alar plate of the prosencephalon expands to form the cerebral hemispheres (the telencephalon) whilst its basal plate becomes the diencephalon. Finally, the optic vesicle grows to form an optic outgrowth.

From the third to the eighth week the face and neck develop.

The inner ear, middle ear and outer ear have distinct embryological origins.

At about 22 days into development, the ectoderm on each side of the rhombencephalon thickens to form otic placodes. These placodes invaginate to form otic pits, and then otic vesicles. The otic vesicles then form ventral and dorsal components.

The ventral component forms the saccule and the cochlear duct. In the sixth week of development the cochlear duct emerges and penetrates the surrounding mesenchyme, travelling in a spiral shape until it forms 2.5 turns by the end of the eighth week. The saccule is the remaining part of the ventral component. It remains connected to the cochlear duct via the narrow ductus reuniens.

The dorsal component forms the utricle and semicircular canals.

The tympanic cavity and eustachian tube are derived from the first pharyngeal pouch (a cavity lined by endoderm). The distal part of the cleft, the tubotympanic recess, widens to create the tympanic cavity. The proximal part of the cleft remains narrow and creates the eustachian tube.

The bones of the middle ear, the ossicles, derive from the cartilages of the pharyngeal arches. The malleus and incus derive from the cartilage of the first pharyngeal arch, whereas the stapes derives from the cartilage of the second pharyngeal arch.

The external auditory meatus develops from the dorsal portion of the first pharyngeal cleft. Six auricular hillocks, which are mesenchymal proliferations at the dorsal aspects of the first and second pharyngeal arches, form the auricle of the ear.[22]

The eyes begin to develop from the third week to the tenth week.

At the end of the fourth week limb development begins. Limb buds appear on the ventrolateral aspect of the body. They consist of an outer layer of ectoderm and an inner part consisting of mesenchyme which is derived from the parietal layer of lateral plate mesoderm. Ectodermal cells at the distal end of the buds form the apical ectodermal ridge, which creates an area of rapidly proliferating mesenchymal cells known as the progress zone. Cartilage (some of which ultimately becomes bone) and muscle develop from the mesenchyme.[22]

Toxic exposures in the embryonic period can be the cause of major congenital malformations, since the precursors of the major organ systems are now developing.

Each cell of the preimplantation embryo has the potential to form all of the different cell types in the developing embryo. This cell potency means that some cells can be removed from the preimplantation embryo and the remaining cells will compensate for their absence. This has allowed the development of a technique known as preimplantation genetic diagnosis, whereby a small number of cells from the preimplantation embryo created by IVF, can be removed by biopsy and subjected to genetic diagnosis. This allows embryos that are not affected by defined genetic diseases to be selected and then transferred to the mother's uterus.

Sacrococcygeal teratomas, tumours formed from different types of tissue, that can form, are thought to be related to primitive streak remnants, which ordinarily disappear.[9][10][12]

First arch syndromes are congenital disorders of facial deformities, caused by the failure of neural crest cells to migrate to the first pharyngeal arch.

Spina bifida a congenital disorder is the result of the incomplete closure of the neural tube.

Vertically transmitted infections can be passed from the mother to the unborn child at any stage of its development.

Hypoxia a condition of inadequate oxygen supply can be a serious consequence of a preterm or premature birth.

Representing different stages of embryogenesis

Early stage of the gastrulation process

Phase of the gastrulation process

Top of the form of the embryo

Establishment of embryo medium

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Human embryonic development - Wikipedia

Life Begins at Fertilization with the Embryo's ConceptionLife Begins at FertilizationThe following references illustrate the fact that a new human embryo,the starting point for a human life, comes into existence with theformation of the one-celled zygote:"Development of the embryo begins at Stage 1 when a sperm fertilizes an oocyte and together they form a zygote."[England, Marjorie A. Life Before Birth. 2nd ed. England: Mosby-Wolfe, 1996, p.31]"Human development begins after the union of male and female gametes or germ cells during a process known as fertilization (conception)."Fertilization is a sequence of events that begins with the contact of a sperm (spermatozoon) with a secondary oocyte (ovum) and ends with the fusion of their pronuclei(the haploid nuclei of the sperm and ovum) and the mingling of theirchromosomes to form a new cell. This fertilized ovum, known as a zygote, is a large diploid cell that is the beginning, or primordium, of a human being."[Moore, Keith L. Essentials of Human Embryology. Toronto: B.C. Decker Inc, 1988, p.2]"Embryo: the developing organism from the time of fertilization untilsignificant differentiation has occurred, when the organism becomesknown as a fetus."[Cloning Human Beings. Report and Recommendations of the National Bioethics Advisory Commission. Rockville, MD: GPO, 1997, Appendix-2.]"Embryo: An organism in the earliest stage of development; in a man,from the time of conception to the end of the second month in theuterus."[Dox, Ida G. et al. The Harper Collins Illustrated Medical Dictionary. New York: Harper Perennial, 1993, p. 146]"Embryo:The early developing fertilized egg that is growing into anotherindividual of the species. In man the term 'embryo' is usuallyrestricted to the period of development from fertilization until theend of the eighth week of pregnancy."[Walters, William and Singer, Peter (eds.). Test-Tube Babies. Melbourne: Oxford University Press, 1982, p. 160]"The development of a human being begins with fertilization, a process by which two highly specialized cells, the spermatozoon from the male and the oocyte from the female, unite to give rise to a new organism, the zygote."[Langman, Jan. Medical Embryology. 3rd edition. Baltimore: Williams and Wilkins, 1975, p. 3]"Embryo: The developing individual between the union of the germ cellsand the completion of the organs which characterize its body when itbecomes a separate organism.... At the moment the sperm cell of thehuman male meets the ovum of the female and the union results in afertilized ovum (zygote), a new life has begun.... The term embryocovers the several stages of early development from conception to theninth or tenth week of life."[Considine, Douglas (ed.). Van Nostrand's Scientific Encyclopedia. 5th edition. New York: Van Nostrand Reinhold Company, 1976, p. 943]"I would say that among most scientists, the word 'embryo' includes the time from after fertilization..."[Dr. John Eppig, Senior Staff Scientist, Jackson Laboratory (BarHarbor, Maine) and Member of the NIH Human Embryo Research Panel --Panel Transcript, February 2, 1994, p. 31]"The development of a human begins with fertilization, a process by which the spermatozoon from the male and the oocyte from the female unite to give rise to a new organism, the zygote."[Sadler, T.W. Langman's Medical Embryology. 7th edition. Baltimore: Williams & Wilkins 1995, p. 3]"The question came up of what is an embryo, when does an embryo exist,when does it occur. I think, as you know, that in development, life isa continuum.... But I think one of the useful definitions that has comeout, especially from Germany, has been the stage at which these twonuclei [from sperm and egg] come together and the membranes between thetwo break down."[Jonathan Van Blerkom of University of Colorado, expert witness onhuman embryology before the NIH Human Embryo Research Panel -- PanelTranscript, February 2, 1994, p. 63]"Zygote. This cell, formed by the union of an ovum and a sperm (Gr. zyg tos, yoked together), represents the beginning of a human being. The common expression 'fertilized ovum' refers to the zygote."[Moore, Keith L. and Persaud, T.V.N. Before We Are Born: Essentials of Embryology and Birth Defects. 4th edition. Philadelphia: W.B. Saunders Company, 1993, p. 1]"The chromosomes of the oocyte and sperm are...respectively enclosed within female and male pronuclei. These pronuclei fuse with each other to produce the single, diploid, 2N nucleus of the fertilized zygote. This moment of zygote formation may be taken as the beginning or zero time point of embryonic development."[Larsen, William J. Human Embryology. 2nd edition. New York: Churchill Livingstone, 1997, p. 17]"Although life is a continuous process, fertilization is a criticallandmark because, under ordinary circumstances, a new, geneticallydistinct human organism is thereby formed.... The combination of 23chromosomes present in each pronucleus results in 46 chromosomes in thezygote. Thus the diploid number is restored and the embryonic genome is formed. The embryo now exists as a genetic unity."[O'Rahilly, Ronan and Mller, Fabiola. Human Embryology & Teratology.2nd edition. New York: Wiley-Liss, 1996, pp. 8, 29. This textbook lists"pre-embryo" among "discarded and replaced terms" in modern embryology,describing it as "ill-defined and inaccurate" (p. 12}]"Almost all higher animals start their lives from a single cell, thefertilized ovum (zygote)... The time of fertilization represents thestarting point in the life history, or ontogeny, of the individual."[Carlson, Bruce M. Patten's Foundations of Embryology. 6th edition. New York: McGraw-Hill, 1996, p. 3]"[A]nimal biologists use the term embryoto describe the single cell stage, the two-cell stage, and allsubsequent stages up until a time when recognizable humanlike limbs andfacial features begin to appear between six to eight weeks afterfertilization...."[A] number of specialists working in the field of human reproduction have suggested that we stop using the word embryoto describe the developing entity that exists for the first two weeksafter fertilization. In its place, they proposed the term pre-embryo...."I'll let you in on a secret. The term pre-embryo has been embracedwholeheartedly by IVF practitioners for reasons that are political, notscientific. The new term is used to provide the illusion that there issomething profoundly different between what we nonmedical biologistsstill call a six-day-old embryo and what we and everyone else call asixteen-day-old embryo."Theterm pre-embryo is useful in the political arena -- where decisions aremade about whether to allow early embryo (now called pre-embryo)experimentation -- as well as in the confines of a doctor's office,where it can be used to allay moral concerns that might be expressed byIVF patients. 'Don't worry,' a doctor might say, 'it's only pre-embryosthat we're manipulating or freezing. They won't turn into real humanembryos until after we've put them back into your body.'"[Silver, Lee M. Remaking Eden: Cloning and Beyond in a Brave New World. New York: Avon Books, 1997, p. 39]

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Life Begins at Fertilization with the Embryo's Conception