Around half of all the eggs produced by both older and younger women could have genetic errors, three new US studies suggest. The findings, reported at the annual meeting of the American Society for Reproductive Medicine (ASRM) in Montreal, Canada, have lead to calls from some fertility experts to screen all embryos used in IVF procedures. Carrying out such 'aneuploidy' screening routinely for all women undergoing fertility treatment would improve success rates, they claim. However, others urge caution until more is known about the potential benefits and harms of the technique.
Aneuploidy, or PGS (preimplantation genetic screening) involves removing a single cell from an embryo to check for chromosome errors that could affect normal development. It is different from PGD, (preimplantation genetic diagnosis) 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.
The HFEA recommends that the technique is only appropriate for women aged over 35 who have undergone many failed IVF attempts, or those who have had several miscarriages. Both can be caused by aneuploidy in the early embryo, the rate of which is thought to increase as eggs age. However, the latest research suggests that about half the embryos produced using eggs from younger women could also be aneuploid.
Researchers at the Shady Grove Center for Preimplantation Genetics in Maryland looked at 275 embryos created using eggs from donors aged between 21 and 31, and found that about half of them had chromosome abnormalities. In another study, a team based at the Huntington Reproductive Centre in California looked at 289 embryos created using eggs from 22 donors under the age of 30, and found that around 42 per cent were aneuploid. Team leader Jeffrey Nelson said the results suggested that PGS should be more widely used. However, the study also revealed a wide variation in the proportion of eggs from each woman that was defective - ranging from 29 per cent to 83 per cent.
A third study, carried out by scientists at Reproductive Biology Associates in Atlanta, compared the rates of aneuploidy between women aged under 35, and those over 38. They found chromosome abnormalities in nearly two-thirds of the embryos produced using eggs from younger women, and in three-quarters of those from older women. Team leader Peter Nagy called the results 'a rewriting' of the textbooks, adding 'these defects should not be present in such a high proportion of patients'. However, none of the studies investigated the possibility that the abnormalities could have originated from the sperm used to create the embryos, or whether the drugs used to obtain eggs for IVF treatment could increase the risk of such errors.
UK expert and British Fertility Society spokesman Stuart Lavery called the findings 'interesting but preliminary', and cautioned against the introduction of widespread embryo screening, because PGS is still a relatively new technique. He told the BBC news website that Belgian researchers are currently carrying out a trial to compare the outcome of IVF treatment both with and without PGS, in young women.
A spokesman for the HFEA said that its expert group would monitor the development of the recent findings, and would listen to the UK's professional bodies if they felt the guidance for PGS should include more groups of women. 'We are concerned that women are properly aware of the potential risks before they choose to have this test and that women and embryos are not tested unnecessarily', he said.