Facial profile markers in second- and third-trimester fetuses with trisomy 18

Objectives To evaluate nasal bone length (NBL), maxilla-nasion-mandible (MNM) angle, fetal profile (FP) line, prenasal thickness (PT), prenasal thickness to nasal bone length (PT: NBL) ratio and prefrontal space ratio (PFSR) as markers of trisomy 18 in the second and third trimesters of pregnancy.Methods The NBL, MNM angle, FP line, PT, PT: NBL ratio and PFSR were measured retrospectively from stored two-dimensional images or three-dimensional volumes of trisomy-18 fetuses, and were compared with our previously reported normal ranges for euploid fetuses. Additional ultrasound findings were noted at initial routine second-trimester scan and at subsequent advanced ultrasound examination performed after referral for karyotyping.Results A total of 43 trisomy-18 fetuses were included in the analysis. At initial examination, median gestational age was 21+2 weeks. NBL and PT were correlated with gestational age (PConclusions The PT: NBL ratio and NBL are robust second-and third-trimester markers for trisomy 18. A negative FP line has a 0% false-positive rate and the potential to differentiate between trisomy 18 and Down syndrome, as in the latter the FP line is often positive. No major anomaly was observed at the initial scan in about a quarter of trisomy-18 fetuses, underlining the role of second-trimester facial marker evaluation. Copyright (C) 2014 ISUOG. Published by John Wiley & Sons Ltd.