10 July 2007
ByAppeared in BioNews 415
A technique used to select IVF embryos most likely to implant and develop could actually reduce success rates, according to a study by Dutch researchers. Preimplantation genetic screening PGS involves removing a single cell from an IVF embryo and testing it for the presence of chromosome aneuploidies - genetic errors that would prevent normal development. The new findings, published in the New England Journal of Medicine and presented at the annual meeting of the European Society of Human Reproduction and Embryology (ESHRE), show that the use of PGS is associated with lower pregnancy and live birth rates.
PGS is distinct from PGD in which an embryo is tested for a single genetic disorder. The Human Fertilisation and Embryology Authority (HFEA) first licensed PGS in 2002, and the first reported UK birth following the use of this technique was in 2003. However, there is continuing disagreement over the utility and efficacy of PGS, with critics saying that its benefits are unproven, while supporters say that it improves the chances of a successful pregnancy in certain groups of patients.
In the latest study, a team of researchers from the Centre for Reproductive Medicine at the University of Amsterdam compared three cycles of IVF in 408 women aged between 35 and 41, 206 of whom had PGS included as part of the treatment. They found that both the pregnancy and live birth rates were lower in the PGS group. Lead author Sebastiaan Mastenbroek said: 'We found that, at 12 weeks, 52 of the women in the PGS group were pregnant (25 per cent), whereas 74 of the control group (37 per cent) had an ongoing pregnancy', adding 'the women in the PGS group also had a significantly lower live birth rate: 49 or 24 per cent, as opposed to 71 or 35 per cent, of the controls'.
The team says there could be several explanations for their results, including the possible effect of removing a single cell from the embryo, or the fact that not all chromosome abnormalities can be detected using PGS - so an apparently normal embryo may still harbour serious genetic errors.
Mastenbroek highlighted the increasingly widespread use of PGS in many IVF clinics. 'The idea of screening embryos for chromosomal abnormalities to increase live birth rates in IVF is very plausible, and women of advanced maternal age are willing to undergo any technique that may provide them with a baby', he said. He also said that more research was needed, particularly in other groups of women who are offered PGS, such as those who suffer recurrent miscarriage or repeated failure of IVF, since evidence for a benefit of PGS in these groups of women is currently still lacking.
Dr Jess Buxton is Contributing Editor at BioNews and a Trustee at the charity that publishes it, the Progress Educational Trust (PET). She is co-author of The Rough Guide to Genes and Cloning (buy this book from Amazon UK) and Human Fertilisation and Embryology: Reproducing Regulation (buy this book from Amazon UK).