Frontomaxillary facial angle in trisomy 21 fetuses at 16-24 weeks of gestation

Objectives: To establish a normal range for the frontomaxillary facial (FMF) angle by three-dimensional (3D) ultrasound imaging and to examine the FMF angle in trisomy 21 fetuses at 16-24 weeks of gestation. Methods: We measured the FMF angle using 3D volumes of the fetal profile obtained with the transducer parallel to the long axis of the nose and at 45° to the palate, which had been acquired from 150 normal fetuses and 23 fetuses with trisomy 21. Results: In the normal group there was no significant association between the FMF angle and gestational age; the mean FMF angle was 83.9° (range, 76.9-90.2°) and the 95^th centile was 88.5°. In 15 (65.2%) of the fetuses with trisomy 21 the FMF angle was greater than 88.5°. Repeatability studies demonstrated that in 95% of cases the difference between two measurements of FMF angle by the same operator and different operators was less than 5°. Conclusions: In the majority of second-trimester fetuses with trisomy 21 the FMF angle is increased.