Down’s syndrome: meeting demands for first-trimester pregnancy screening

Down’s syndrome is a genetic disorder that affects approximately one in 1000 live births in the UK,1 and occurs as a result of the presence of an extra copy of some or all of the genetic material on chromosome 21 (trisomy 21). It is associated with a range of distinctive physical features and moderate to severe learning difficulties, as well as a number of additional health issues such as congenital heart disease, sight and hearing problems and Alzheimer’s disease.

The risk of Down’s syndrome increases with maternal age (one in 30 in women aged over 451), but affected pregnancies can occur in women of any age. The condition is diagnosed by chorionic villus sampling (CVS) or amniocentesis. These methods are invasive and carry the risk of procedure-induced loss of the fetus. It is important, therefore, to limit such diagnostic tests to those at highest risk of an affected pregnancy.

Screening pregnancies on the basis of maternal age alone will only detect around 30% of affected pregnancies and so additional markers have been introduced over the years to increase the detection rate of Down’s syndrome screening methods. Screening for Down’s syndrome using multiple markers is now widely accepted as part of routine antenatal care.