Screening for trisomies 21, 18 and 13 by maternal age, fetal nuchal translucency, fetal heart rate, free β-hCG and pregnancy-associated plasma protein-A

BACKGROUND: A beneficial consequence of screening for trisomy 21 is the early diagnosis of trisomies 18 and 13. Our objective was to examine the performance of first-trimester screening for trisomies 21, 18 and 13 by maternal age, fetal nuchal translucency (NT) thickness, fetal heart rate (FHR) and maternal serum-free beta-hCG and pregnancy-associated plasma protein-A (PAPP-A). METHODS: Prospective screening for trisomy 21 by maternal age, fetal NT, free beta-hCG and PAPP-A at 11(+0)-13(+6) weeks in singleton pregnancies, including 56376 normal cases, 395 with trisomy 21, 122 with trisomy 18 and 61 with trisomy 13. Risk algorithms were developed for the calculation of patient-specific risks for each of the three trisomies based on maternal age, NT, FHR, free beta-hCG and PAPP-A. Detection (DR) and false positive rates (FPR) were calculated and adjusted according to the maternal age distribution of pregnancies in England and Wales in 2000-2002. RESULTS: The DR and FPR were 90 % and 3 %, respectively, for trisomy 21, 91 % and 0.2 % for trisomy 18 and 87 % and 0.2 % for trisomy 13. When screen positivity was defined by an FPR of 3 % on the risk for trisomy 21 in conjunction with an FPR of 0.2 % on the maximum of the risks for trisomies 13 and 18, the overall FPR was 3.1% and the DRs of trisomies 21, 18 and 13 were 91%, 97% and 94%, respectively. CONCLUSIONS: As a side effect of first-trimester screening for trisomy 21, similar to 95% of trisomy 13 and 18 fetuses can be detected with an 0.1 % increase in the FPR.