Down syndrome screening in multiple pregnancies by nuchal translucency measurement

Various non-invasive screening methods for Down syndrome have been introduced in clinical practice during the last two decades. Specific problems were encountered when these methods were applied for multiple pregnancies (twins and high-order multiples). The aim of the current review is to explore these issues and propose an adjusted methodological approach for this highly selected population. Overall, more women with twin pregnancies (mainly those who conceived via assisted reproduction) are found to be false-positive for Down syndrome. This is because the standard screening algorithms include maternal age. In addition, mid-trimester maternal serum screening is associated with a higher false-positive rate, secondary to changes in the fetoplacental endocrinologic metabolism in assisted reproduction pregnancies. Therefore, in multiple pregnancies, mid-trimester maternal serum screening is of limited clinical value. In those pregnancies, screening for Down syndrome by means of nuchal translucency measurements at 10–14 weeks is associated with a lower false-positive rate than mid-trimester serum screening. Nuchal translucency measurement is among the best available and most efficient screening methods for multiple pregnancies. This method for screening enables us to specifically identify those fetuses at high risk of Down syndrome and other anomalies and thus contribute for a better outcome. In addition, it should be systematically performed before any fetal reduction in high-order multiples is planned.