Embryo screening makes IVF pregnancy harder

LYON: An older woman's slim chances of getting pregnant by IVF could be made worse if embryos are screened for defects before being implanted in the womb.

Pregnancy and live birth rates were substantially lower among women whose embryos were screened compared with those whose were not, according to a study presented yesterday at a meeting of the European Society of Human Reproduction and Embryology in Lyon, France.

The findings, which were questioned by some experts, suggest genetic screening should not be a routine part of fertility treatment for women over 35.

"Based on our research, I would say skip the pre-genetic screening and stick with regular in-vitro fertilisation," said Sebastiaan Mastenbroek from the Centre for Reproductive Medicine at the University of Amsterdam.

In the study, published in the New England Journal of Medicine, Dr Mastenbroek and colleagues tried to determine the value of pre-genetic screening, a process that involves taking a single cell from a developing embryo to look for chromosomal defects that could lead to problems such as Down syndrome.

Doctors have tended to believe that selecting the most promising embryos gives older women a better chance of getting pregnant.

But some experts have expressed concern that fertility centres promote the genetic tests because they generate profit. A single test costs up to $5800.

"This is the first study that has tried to determine for patients, if they put their money down, whether they will take a baby home," said Peter Braude, professor of obstetrics and gynaecology at London' King's college.

The answer, Dr Braude said, was: not necessarily. Just why screening cuts the chance of a viable pregnancy is unclear, but Dr Mastenbroek said the test itself might be to blame.

"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," he said yesterday.

Usually, embryos will have reached the eight-cell stage of development by day three but sometimes there may be as few as four cells, which could in theory make the procedure riskier. Other factors may be the limited number of chromosomes that can be analysed, and that many embryos are "mosaic", where a single cell does not reflect the genetic make-up of the whole.

The study involved 408 women, aged 35-41 and undergoing three cycles of IVF. The Dutch researchers tested embryos from half the women. About half were assigned to have embryos screened. Those who had the screening had a substantially lower pregnancy rate: 25per cent versus 37per cent.

More than 60per cent of the embryos implanted in women who had them screened were abnormal. In this study, having their embryos screened did not help older women get pregnant.

Fertility experts said more research was needed into the benefits, if any, of pre-implantation genetic diagnosis.

source : www.theaustralian.news.com.au