[Prenatal screening: the example of Down's syndrome screening]

Abstract

Prenatal screening for Down's syndrome initially targeted high-risk pregnant women (> 35 years old). However, the vast majority of babies with Down's syndrome are born to younger women (as the majority of babies are born in this age category). It was first discovered that some serum analytes were altered in pregnancies affected with Down's syndrome (triple test). In the nineties, the association between an increased nuchal translucency measurement and trisomy 21 was noted. The use of this measurement in combination with serum markers has enabled an increased detection rate but still at the cost of a false positive rate of around five percent (combined test). Recently, major advances in sequencing technologies have allowed reasearchers to make use of the cell free fetal DNA in maternal blood. This new test (named non invasive prenatal test) made it into clinical use as early as 2011 in some countries. Its sensitivity is above 99 % for trisomy 21 and the false positive rate is very low. It is risk-free and much more accurate than previous approaches. It is largely favored over an invasive test by high risk women (advanced maternal age or high-risk combined test). Its use is still restricted by a high cost which is for the moment still entirely beared by the patient. The availability of NIPT in our routine practice and the increased complexity of screening options have highlighted the need for a more dedicated counselling consultation before Down's syndrome screening is performed.