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.