Screening for Chromosomal Abnormalities by First Trimester Combined Screening and Noninvasive Prenatal Testing

Objective: To examine combined first trimester screening (FTS), noninvasive prenatal testing (NIPT) and a two-step policy that combines FTS and NIPT in screening for aneuploidy. Materials and Methods: Retrospective study involving 21052 pregnancies where FTS was per- formed at the Praxis Praenatal.de in Duesseldorf, Germany. In each case, the sum risk of trisomy 21, 18 and 13 was computed. We assumed that NIPT detects 99%, 98%, 90% and 99% of cases with trisomy 21, 18, 13 and sex chromosomal abnormalities and that the false-positive rate is 0.5%. The following screening policies were examined: NIPT or FTS with s…