The number of Down's syndrome pregnancies has risen sharply over the last 20 years as women have opted to have children later, according to new research published in the British Medical Journal.
Over the same period, there have been major improvements in pre-natal screening for the condition and an increase in the number of women being screened.
This means the overall number of babies being born with Down's syndrome has remained almost level at around 750 babies each year.
This research is based on the National Down Syndrome Cytogenetic Register -- a unique resource held at Queen Mary, University of London which has recorded almost all Down's syndrome pregnancies and births in England and Wales since 1989.
The study's author is Joan Morris, Professor of Medical Statistics at Queen Mary, University of London. She said: "What we're seeing here is a steep rise in pregnancies with Down's syndrome but that is being offset by improvements in screening. It was thought that these improvements would lead to a decrease in the number of births with Down's syndrome. However due to increases in maternal age this has not occurred.
"Other researchers here at Queen Mary have made major improvements to the Down's screening test and it's become more widely available over the last 20 years. This means we're picking up more Down's pregnancies."
Analysis of the data has revealed a 71 per cent increase in the number of Down's syndrome pregnancies and births, which the researchers believe is primarily the result of women delaying having children.
The risk of having a baby with Down's syndrome is just one in 940 for a woman aged 30. By age 40 the risk rises to one in 85.
The number of babies born with Down's syndrome has fallen by just one per cent since 1989. There has been a sharp increase in the proportion of Down's syndrome pregnancies in women under the age of 37 being detected by screening -- rising from 3 per cent to 43 per cent -- while the figure in older women has stayed constant at around 70 per cent. This is a reflection of improvements in screening, particularly for younger women.
The proportion of couples diagnosed with a Down's syndrome pregnancy who decide to terminate has also remained constant at 92 per cent.
The National Down Syndrome Cytogenetic Register is funded by The Healthcare Quality Improvement Partnership (HQIP) until March 2010. The researchers are urgently seeking more funding to continue this 20-year survey.
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