Down's syndrome screening in pregnancies after assisted reproductive techniques: an update.

Assisted reproductive techniques have increased the number of pregnant women beyond the age of 35 years and the incidence of multiple pregnancies. Various non-invasive screening methods for Down's syndrome were introduced in clinical practice during the past two decades. Specific problems were encountered when these methods were applied for pregnancies achieved by assisted reproduction treatment and the aim of this review is to explore these issues and propose an adjusted methodological approach for this highly selected population. Overall, more women with assisted reproduction singleton pregnancies are found to be false-positive for Down's syndrome. This is because standard screening algorithms include maternal age. In addition, mid-trimester maternal serum screening is associated with a higher false-positive rate. This is due to changes in the feto-placental endocrinological metabolism in pregnancies achieved by assisted reproduction treatment. Ultrasound screening of Down's syndrome by means of nuchal translucency (NT) measurements at 10-14 weeks is associated with a lower false-positive rate than mid-trimester serum screening. The lowest false-positive rates reported in singleton pregnancies are observed when serum and nuchal translucency screening are combined at 10-14 weeks. In multiple pregnancies, mid-trimester maternal serum screening is of limited clinical value. Nuchal translucency measurement is among the best available and is the most efficient screening method for multiple pregnancies. This sonographical method for screening enables specific identification of those fetuses at high risk of Down's syndrome and other anomalies, and thus contributes to a better outcome. Therefore, it should be systematically performed before any fetal reduction in high-order multiple pregnancies is planned.