From 1989 through 2008, better antenatal screening for Down syndrome kept the number of affected live births constant despite a shift toward older maternal age at delivery.
The U.K.'s National Down Syndrome Cytogenetic Register has received data on all ante- or postnatal diagnoses of Down syndrome in England and Wales since 1989. During that time, incidence of antenatally diagnosed Down syndrome rose by 71%. The largest increase occurred after 2001, when the U.K. National Screening Committee recommended that all women be offered antenatal screening; in addition, the number of Down syndrome live births fell by 1%. From 1989 to 2008, mean maternal age rose from 30.6 to 34.4. Among women 37 or older, the proportion of Down pregnancies that were diagnosed antenatally remained constant at 70%, whereas in younger women the proportion of Down pregnancies diagnosed antenatally increased from 3% in 1989 to 43% in 2008;…