<prompt> Detection of aneuploidy in 1st trimester:hCG and PAPP-AhCG and AFPhCG, PAPP-A and AFPAFP and estriol  <response>: Ans. A. hCG and PAPP-ARef: Williams 24thed, p289Table 2: Selected Down syndrome screening strategies and their detection rateStrategyAnalytesDetection Rate3 First-trimester screenNT, PAPP-A, and hCG or free p-hCG79-87NTNT alone64-70Triple testMSAFP hCG OR free p-hCG, uE361-70Quadruple Quad testMSAFP, hCG or free p-hCG, uE3, inh74-81Integrated screenFirst-trimester screen and Quad test; results withheld until Quad test completed94-96Stepwise sequentialFirst-trimester screen and Quad test 1 offered diagnostic test after first-trimester screen 99 proceed to Quad test, results withheld until Quad test completed90-95Contingent sequential screenFirst-trimester screen and Quad test 1 offered diagnostic test after first-trimester screen 15 proceed to Quad test; results withheld until Quad test completed84 have no additional test after first trimester screen88-94Cell-free fetal DNA testing high-risk pregnanciesNo analytes--massively parallel genomic sequencing98aBased on a 5 positive screen rate.Free b-hCG free b-subunit hCG; hCG human chorionic gonadotropin, inh dimeric inhibin a;MSAFP maternal serum alpha-fetoprotein; NT nuchal translucency; PAPP-A pregnancy-associated plasma protein-A; uE3 unconjugated estriol. 