Changes in maternal age in England and Wales--implications for Down syndrome.

The risk of having a pregnancy with Down syndrome increases with maternal age. The percentage of all births in England and Wales to mothers aged 35 and over increased from 9% in 1989 to 19% in 2003. A 51% increase in the numbers of pregnancies with Down syndrome has been observed over the same time period (from 954 to 1440). Due to improvements in antenatal screening for Down syndrome and the subsequent termination of affected pregnancies, the total number of births with Down syndrome decreased from 770 in 1989 to 609 in 2003. However the number of births with Down syndrome to women aged 35 and over increased from 186 in 1989 to 310 in 2003 because of the increasing number of pregnancies amongst these women.