The number of diagnoses of Down's syndrome has increased by almost three quarters (71%) from 1989/90 to 2007/08, largely due to the considerable increase in the number of older mothers over this period. However, the number of babies born with this condition during the same period fell by 1% because of antenatal screening and subsequent terminations, finds research published on bmj.com today.
Researchers from Barts and The London Medical School analysed data held on the National Down Syndrome Cytogenetic Register (NDSCR) since it was set up in January 1989. The register currently holds anonymous data on over 26,000 cases of Down's syndrome diagnosed antenatal or postnatally in England and Wales, this is around 93% of all diagnosed Down's births and pregnancy terminations in both countries.
Their results show that while there has been a stark increase in the proportion of younger women (below the age of 37) opting for screening (3% to 43%), the proportion of older women deciding to be screened has stayed constant at around 70%, despite improved tests.
And for all women with an antenatal diagnosis of Down's syndrome, the proportion who decided to terminate the pregnancy has also remained constant at around 9 in 10 (92%).
Lead author, Professor Joan Morris, says that, given older women have a far greater chance of having a baby with Down's (the risk for a 40 year old mother is 16 times that for a 25 year old mother), more research is needed to find out why around 30% of older women decide not to be tested. "It is important to ascertain whether the decision is an informed one and, if not, to address the lack of information," she says.
The authors conclude that as more women are having children later in life and a significant proportion of these mothers are deciding against screening "a large number of births with Down's syndrome are still likely, and that monitoring of the numbers of babies born with Down's syndrome is essential to ensure adequate provision for their needs."