In a general population, antenatal screening of Down syndrome is by:

Serum biomarker tests for Downs Syndrome screening Dual marker: PAPP-A + free b HCG (along with nuchal transluscency) Triple marker: free b HCG + AFP + unconjugated estriol quadruple marker: free b HCG + AFP + Unconjugated estriol + Inhibin A First-trimester screening at 11 to 14 weeks' gestation, using the fetal nuchal translucency measurement together with serum analytes like PAPP-A and HCG levels , has achieved Down syndrome detection rates comparable to those for second-trimester screening in women younger than 35 years. Combinations of first- and second-trimester screening yield down syndrome detection rates as high as 90 to 95 percent Maternal serum cell-free fetal DNA testing for trisomy 21, 18, and 13 has become available as a screening test for high-risk pregnancies, with a 98-percent detection rate and a false-positive rate of 0.5 percent