The fetal frontomaxillary facial angle in normal and trisomy 21 ultrasounds at 11-13⁺⁶ weeks of gestation: Findings among the ethnic Chinese compared with Caucasian

Objective: The aim of this research was to compare the fetal frontomaxillary facial (FMF) angle between normal and trisomy 21 fetuses at 11⁺⁰-13⁺⁶weeks gestation in a Chinese population. Methods: A prospective observational study was performed that included 640 euploid and 45 trisomy 21 singleton pregnancies undergoing first trimester ultrasound screening between 11 and 13⁺⁶weeks of gestation. The FMF angle was measured in the midsagittal plane using the standard technique. Results: The fetal mean FMF angle decreased with the increasing crown-rump length (CRL) from 88.6°at a CRL of 45mm to 78.5° at a CRL of 84mm (FMF angle=100.212-0.258×CRL, R²=0.222, p<0.001). The overall mean FMF angle in the euploid population was 82.9°±4.1° and in trisomy 21 cases, 92.3°±5.2°. Conclusions: Fetal FMF angle is affected by gestational age in a Chinese population, although it remains a significant predictor of fetal trisomy 21.