Screening embryos for chromosomal abnormalities

In this week's BioNews, we report on the issuing of licenses to two UK IVF clinics to provide a procedure known as aneuploidy screening. The aim of this technique, which is a variation of PGD (preimplantation genetic diagnosis), is to screen out embryos that, because of chromosomal abnormality, are unlikely to survive in the womb. But critics are worried about how the screening technique might be used in the future.

At present, aneuploidy screening is focused upon early embryos that are so abnormal that they are unlikely to develop into viable fetuses. The patients being offered treatment will have experienced either a number of miscarriages or repeated failure to conceive after IVF treatment. As such, these people are seeking treatment to help them have a child that nature has denied them.

However, aneuploidy screening can also be used to screen out embryos which may result in a baby, but one which is affected by a chromosomal abnormality, such as Down's syndrome. Whilst some embryos carrying non-fatal chromosomal abnormalities are probably lost through early miscarriage, many are not and can lead to the birth of affected babies. Would it be right for embryo screening techniques to be used in the UK to avoid the birth of such babies, as they are in other countries such as the United States?

If embryo screening were used in the UK for this purpose, it would form part of prenatal screening services available to women. Much of the screening and testing available during pregnancy is aimed at detecting the presence of chromosomal abnormalities, such as Down's syndrome, in fetuses. Demand for these services appears to be high. Most women (estimates vary from 80 to 92 per cent) who are told that their baby will have Down's syndrome, for instance, decide to have a termination of pregnancy. It's hard to see how screening for chromosomal abnormalities before a pregnancy has started is any different from screening for them after it has started.

As it happens, demand for screening before pregnancy might not be so high. Most women don't already know that they are at high of risk of having a baby with a chromosomal abnormality, so they will not be requesting embryo screening. Even those who know they are at high risk might consider embryo screening to be too invasive, too expensive and not successful enough to consider using it. But there might be some women - older women already having IVF, for instance - who will see this as a worthwhile addition to reproductive medicine.