[First-trimester screening for trisomies 18 and 13 with the combined use of the risk algorithms for trisomy 21, 18 and 13].

PURPOSE: Assessment of first-trimester combined screening for trisomy 18 and 13 with the combined use of the risk algorithms for trisomy 21, 18 and 13.

MATERIALS AND METHODS: First-trimester combined screening based on maternal and gestational age, fetal NT, PAPP-A and free β-hCG was assessed in 39 ,004 pregnancies. Patient-specific risks for trisomy 21, 18, 13 were computed based on the current FMF London algorithm.

RESULTS: The study population consisted of 38 ,751 singleton pregnancies including 39 cases with trisomy 18 or 13. In the aneuploid group, median delta NT was 0.72 mm, PAPP-A was 0.21 MoM and free β-hCG was 0.33 MoM. Although only 41 % of the NT measurements of fetuses with trisomy 18 or 13 were above the 95th percentile, the detection rates for trisomy 18 or 13 were 82 % with the trisomy 18/13 algorithm and 56.4 % with the trisomy 21 algorithm. The respective false-positive rates were 0.7 % and 4.7 %. The combination of the trisomy 18/13 and the trisomy 21 algorithm with the same cut-offs led to a detection rate of 94.9 % at an overall false-positive rate of 5.0 %.

CONCLUSION: Despite a substantial underestimation of the fetal NT, the combined use of the trisomy 18/13 and the trisomy 21 algorithm of the FMF London leads to a detection rate for trisomy 18/13 of about 95 % for a false-positive rate of 5.0 %.