Research published today on bmj reports that the number of diagnoses of Down's syndrome has increased by almost 71 percent from 1989-90 to 2007-08. This is mostly due to the considerable increase in the number of elder mothers over this period. Yet during the same period, the number of babies born with this condition fell by one percent because of antenatal screening and subsequent terminations.

Researchers from Barts and The London Medical School explored this trend. Data recorded since January 1989 from the National Down Syndrome Cytogenetic Register (NDSCR) was analyzed. Currently the register holds anonymous data on over 26,000 cases of Down's syndrome diagnosed antenatal or postnatally in England and Wales. This accounts for 93% of all diagnosed Down's births and pregnancy terminations in both countries.

Findings indicate that there has been a sharp increase of 3 to 43 percent in the proportion of younger women (below the age of 37) opting for screening. However despite improved tests, the proportion of older women deciding to be screened has stayed invariable at around 70 percent.

In the case of women with an antenatal diagnosis of Down's syndrome, the proportion who decided to terminate the pregnancy has also remained constant at around 92 percent (9 in 10).

Lead author, professor Joan Morris explains that older women have a far greater chance of having a baby with Down's since the risk for a 40 year old mother is 16 times that for a 25 year old mother. There is a need for further research to find out why around 30 percent of older women decide not to be tested. She says: "It is important to ascertain whether the decision is an informed one and, if not, to address the lack of information."

The authors say in closing that as more women are having children later in life and a considerable 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."

"Trends in Down's syndrome live births and antenatal diagnoses in England and Wales from 1989 to 2008: analysis of data from the National Down Syndrome Cytogenetic Register" Joan K Morris, professor of medical statistics, Eva Alberman, emeritus professor
BMJ 2009; 339:b3794
doi:10.1136/bmj.b3794
bmj

Stephanie Brunner (B.A.)