01 November 2009
ByAppeared in BioNews 532
According to figures published in the British Medical Journal last week, the number of diagnoses of Down syndrome in babies and fetuses in England and Wales has risen by 71 per cent over the past 20 years. This is attributed to an increase in maternal age over this period. A concurrent increase in terminations of affected pregnancies as a result of improved prenatal screening methods has meant that numbers of live births with Down syndrome have fallen by one per cent, whereas they would have risen by 48 per cent without any screening.
These numbers are surprising, as it was thought that prenatal screening would reduce the live birth rate, whereas this reduction is actually compensated entirely by the rise in occurrence of the condition due to late motherhood. The risk of having a child with Down syndrome is one in 85 for a 40 year old mother, a more than tenfold increase from age 30, when it is only one in 940.
At the moment, screening for Down syndrome is a two step process. Around week 12 of the pregnancy, blood and ultrasound tests can show if the fetus is at high risk for Down syndrome, meaning the risk is between 0.4 and 50 per cent. In this case, a test called amniocentesis can be performed, which provides a more definite result, but this comes with a roughly one per cent risk of miscarriage. All tests are voluntary.The study also shows that the rate at which women who learn they are carrying a Down syndrome fetus and choose to terminate their pregnancy has remained constant, at 92 per cent, and that 30 per cent of pregnant women choose not to be tested. As a result, organisations supporting people with Down syndrome and their families have voiced their concern that women undergoing these tests are not adequately informed. One parent of a Down syndrome child told BBC Breakfast: 'Because you have a test [during pregnancy] you think that it must be a terrible thing if it happened. There's no qualifying information and I think that would be really useful to get that and it might affect a lot of people's decision as to whether they could live with that.'