Screening IVF embryos 'can damage birth chances'

A technique for testing the health of an IVF embryo makes it less, rather than more, likely that a woman will have a successful pregnancy and birth, a study has found.

The test, which involves taking and analysing a single cell from an early embryo, appears to increase the risk of failed pregnancies or stillbirths, despite being a tool for detecting abnormal chromosomes.

Scientists who carried out the study warned yesterday that preimplantation genetic screening (PGS) should not be carried out routinely on older women who are trying to have a baby through IVF treatment.

They based their warning on a study of 408 women aged beween 35 and 41, half of whom were given PGS before their IVF embryos were implanted into the womb. The scientists then compared rates of pregnancies and live-births between the two groups.

"We found that, at 12 weeks, 25 per cent of the women in the PGS group were pregnant, whereas 37 per cent of the control group had an ongoing pregnancy," said Sebastiaan Mastenbroek of the University of Amsterdam.

"And the women in the PGS group also had a significantly lower live-birth rate - 24 per cent, as opposed to 35 per cent, of the controls," he said.

The study, published in the New England Journal of Medicine, is the first to look at the effects of PGS on the pregnancies and births of a large group of women. It has not, however, explained why PGS should increase the risk of a failed pregnancy.

"It is possible that the biopsy of a cell from an early embryo on day three after conception hampers the potential of an embryo to successfully implant, though the effect of biopsy alone on pregnancy rates has not been studied," Mr Mastenbroek said.

Another possibility is that PGS is not picking up all the abnormal chromosomes of an embryo, which means that defective embryos are still getting through the screening process.

PGS is increasingly being used in fertility centres around the world to screen IVF embryos for chromosome defects before implantation. Older women are at higher risk of chromosome abnormalities and as a result they are often offered PGS.

Professor Alan Handyside of the London Bridge Fertility Centre, who pioneered the development of PGS, said the technique was very effective when properly targeted on high-risk patients.

"It is dangerous for people to be saying that PGS has no clinical benefit," he said. "This is simply not our experience and may deprive high-risk patients of treatment they need."