Multicenter study of first‐trimester screening for trisomy 21 in 75 821 pregnancies: results and estimation of the potential impact of individual risk‐orientated two‐stage first‐trimester screening

First-trimester combined screening for trisomy 21 is associated with a detection rate of about 90% for a false-positive rate of 5%. Individual risk-orientated two-stage screening for trisomy 21 can potentially identify, in the first trimester of pregnancy, more than 90% of affected fetuses for a false-positive rate of 2-3%.