Lyon, France - Screening embryos for chromosomal defects, a fast-growing practice aimed at helping older women to have a baby, in fact reduces the chance of a successful pregnancy, doctors reported on Wednesday.

The process, called preimplantation genetic screening (PGS), entails taking a cell from a lab-dish embryo on its third day of development, and testing a number of its chromosomes for any abnormalities.

The goal is to filter out embryos that could develop abnormally and trigger miscarriage, leaving only the fittest for transfer to the uterus.

But Dutch fertility experts, led by the University of Amsterdam's Sebastiaan Mastenbroek, said their own large-scale investigation found PGS in fact lowers the success rate.

They looked at 408 women, aged 35 to 41 who had had three cycles of in-vitro fertilisation (IVF).

One randomly-selected group of 206 women was given PGS, while the other 202 were not given PGS, thus acting as a "control" group, or comparison.

"We found that, at 12 weeks, 52, or 25 percent, of the women in the PGS group were pregnant, whereas 74, or 37 percent, of the control group had an ongoing pregnancy," Mastenbroek said.

"And the women in the PGS group also had a significantly lower live birth rate - 49, or 24 percent, as opposed to 71, or 35 percent, of the controls."

The research was unveiled at the annual conference of the European Society of Human Reproduction and Embryology (ESHRE), taking place in this southeastern French city. It was also published simultaneously in the New England Journal of Medicine.

PGS is a relatively new technique that is in increasing use in IVF centres around the world. But the process also has stirred concerns that it encourages eugenics, and some countries ban it or restrict its use to embryos from parents who have an inherited disease.

Mastenbroek said there could be several explanations why PGS had failed in these older women.

One was that the taking of the sample cell, a process called a biopsy, could somehow affect the embryo's potential to develop normally, he said.

Another possible cause was that the number of chromosomes which are analysed was too small. This meant that embryos which had been certified as normal were in fact abnormal, because they carried one or more flawed chromosomes that had not been tested.

A third explanation could be that the biopsied cell may be an odd-one-out - it may not be representative of the chromosomal composition of the whole embryo.

Mastenbroek said further work was needed to see whether PGS was effective or not in other groups of women, such as those who suffer recurrent miscarriage.

But, he said, the results of his research suggest PGS should not be carried routinely for older would-be mothers.

Meanwhile, British and Danish researchers said infertile women who turn to so-called complementary therapies such as reflexology and nutritional supplements to support their IVF treatment also have a lower chance of pregnancy.

Their study of 818 Danish women in the 12 months following the start of IVF found that those who used complementary therapies had a 20-percent lower pregnancy success rate.

"It may be that complementary therapies diminish the effectiveness of medical interventions, as has been shown in previous research," said Jacky Boivin of Cardiff University, Wales.

"Or it may simply be that persistent treatment failure encourages women to seek out CATs because they are more willing to try anything to get pregnant."

The next step is to study the same group over five years to get a longer-term view of the pregnancy rate.

"It is important to do this because we are concerned that, with persistent treatment failure, women might become more and more susceptible to deceptive advertising about ineffective CATs or other unproven treatments," Boivin said.

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'Screening cuts chances for healthy babies' - Independent Online