The Effect of Ethnicity on 2D and 3D Frontomaxillary Facial Angle Measurement in the First Trimester

Objectives. To determine the existence and extent of ethnic differences in 2D or 3D fetal frontomaxillary facial angle (FMFA) measurements. Methods. During routine 11–14 weeks nuchal translucency screening undertaken in a private ultrasound practice in Sydney, Australia, 2D images and 3D volumes of the fetal profile were collected from consenting patients. FMFA was measured on a frozen 2D ultrasound image in the appropriate plane and, after a delay of at least 48 hours, was also measured on the reconstructed 3D ultrasound volume offline. Results. Overall 416 patients were included in the study; 220 Caucasian, 108 north Asian, 36 east Asian and 52 south Asian patients. Caucasians had significantly lower median FMFA measurements than Asians in both 2D (2.2°; ) and 3D (3.4°; ) images. Median 2D measurements were significantly higher than 3D measurements in the Caucasian and south Asian groups ( and ), but not in north and east Asian groups ( and ). Conclusions. Significant ethnic variations in both 2D and 3D FMFA measurements exist. These differences may indicate the need to establish ethnic-specific reference ranges for both 2D and 3D imaging. 1. Introduction Ultrasound-based screening for fetal aneuploidy in the first trimester has developed rapidly over the past 20 years. The original observation that faces of Down syndrome individuals were flat led to the investigation of frontomaxillary facial angle (FMFA) measurement as a risk factor for trisomy 21 [1]. Reference ranges for FMFA using offline three-dimensional (3D) reconstruction software were developed in the first trimester identifying the 95th percentile measurement as 85° [2]. In a previous study, we demonstrated that 2D FMFA measurements were similar, but not equivalent, to those obtained by the 3D method; thus, normative data would need to be collected from the normal population separately for both 2D and 3D [3]. Given the potential ethnic variations, normative data from local populations may also be necessary. A recent study has cast doubt on the efficacy of first trimester FMFA measurement as a screening method for Down syndrome in an Asian population. Kwon and colleagues demonstrated that 3D FMFA measurements in the normal Korean population were substantially wider than the previously reported mean which would increase the screening false positive rate [4]. A study by Chen et al. [5] contradicts this finding in the Asian population, as the difference in FMFA measurements between Caucasian and Chinese patients was thought to be so small that it was not clinically significant. Given the