The proportions of Down's syndrome pregnancies detected prenatally in England and Wales from 1989 to 2004

Abstract

The proportion of Down's syndrome pregnancies detected prenatally in England and Wales is lower in younger mothers than in older mothers. This paper examines the reasons for this apparent age inequality. We used data from the National Down Syndrome Cytogenetic Register (NDSCR) to examine the time trend of the proportion of Down's syndrome pregnancies diagnosed prenatally according to maternal age over the years 1989-2004 in England and Wales. A lower proportion of younger mothers had their Down's syndrome pregnancy detected prenatally than older mothers; however, this gap has been closing over time. For example, for mothers under 25 years of age only 13% of Down's syndrome pregnancies were detected prenatally from 1989 to 1992, with this figure rising to 34% in 2001-2004, compared with proportions of 74% in both periods for mothers over 44 years of age. A lower uptake of screening among younger women could not explain these differences. The differences in detection rates of the screening methods according to maternal age, particularly of the older screening tests, could account for these differences. The closing gap between the proportions of younger and older women having their affected pregnancy prenatally diagnosed is a confirmation of the improvement of screening methods over time.