Biochemical screening for Down’s syndrome in the first trimester of pregnancy

Abstract

Down’s syndrome (DS) is the commonest single cause of severe mental retardation and accounts for just under a third of all cases. Until the late 1980’s population screening was based on offering amniocentensis to older women. This made little impact on the prevalence of DS because the majority (approximately 70%) of babies with DS are born to women under the age of 35 (Figure 1).