Aneuploidy incidence rates and performance of conventional screening approaches in the first and second trimester for a general population.

^ Conventional screening based on maternal age, nuchal translucency, maternal serum pregnancy-associated plasma protein A [PAPPA] and free beta human chorionic gonadotropin [hCG] at 12 weeks gestational age. * NIPT sensitivity and specificity was based on pooled data from 19 published studies (see S2 Table); NIPT sensitivity and specificity was considered to be independent of pregnancy stage and maternal prior risk. † First trimester sensitivity for trisomy 13 screening is based on the algorithm developed for trisomy 18 screening [30]. ‡ Second trimester sensitivity for trisomy 13 screening is assumed to be equal to the proportion of trisomy 13 affected pregnancies serendipitously identified as a false positive in Down syndrome and trisomy 18 screening. § No specific screening protocols exist for trisomy 13 and monosomy X. Aneuploidy incidence rates and performance of conventional screening approaches in the first and second trimester for a general population.