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Late motherhood causes steep rise in Down syndrome diagnoses

1 November 2009
Appeared 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.'
Delayed motherhood behind increase in Down's syndrome babies, research says
The Guardian |  27 October 2009
Increase In Down Syndrome Offset By Better Screening
ScienceDaily |  26 October 2009
Steep rise in Down's pregnancies
BBC News Online |  27 October 2009
Surge in Down’s pregnancies is matched by surge in terminations
The Times |  27 October 2009
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26 May 2009 - by Rosie Beauchamp 
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12 May 2009 - by Ben Jones 
The effectiveness of a prenatal test for Down syndrome has been thrown into doubt after its developers, Sequenom, admitted that study data had been 'mishandled' by its employees. The company, which had been producing apparently strong results in house for its DNA and RNA blood testing products...
30 November 2008 - by Sarah Pritchard 
Numbers of babies being born in the UK with Down's syndrome are increasing to higher levels than before prenatal screening was widely available. Births of Down's syndrome babies have risen to a figure of 749 in 2006 compared with 717 in 1989, the year screening was introduced...
13 October 2008 - by Lorna Stewart 
Scientists at Stanford University in California, US have developed a new non-invasive prenatal test for Down's syndrome. Stephen Quake and colleagues successfully identified presence and absence of fetal chromosomal abnormality in 18 pregnant women from maternal blood samples. The work is published this month in the journal...
8 January 2007 - by Dr Jess Buxton 
The American College of Obstetricians and Gynecologists (ACOG) has recommended that all pregnant women should be offered screening for Down syndrome, regardless of their age. Lead author Dr Deborah Driscoll said last week that 'this new recommendation says that the maternal age of 35 should no...
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