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; 92% of all women terminated their pregnancies after receiving antenatal diagnoses of Down syndrome.

Comment: Whereas the growing incidence of Down syndrome diagnoses parallels the rise in maternal age, the actual annual number of live Down syndrome infants born in England and Wales has remained steady during the past 20 years, primarily because most affected pregnancies are terminated. The American College of Obstetricians and Gynecologists (Obstet Gynecol 2007; 109:217) recommends that all pregnant women, regardless of age, be offered antenatal Down syndrome testing before the 20th week of gestation. Because women in the U.S. might be less likely than those in the U.K. to terminate Down syndrome pregnancies, similar demographic shifts toward older maternal age could result in comparatively higher rates of Down syndrome live births in the U.S.