INTRODUCTION: The aim of this study is to (i) directly compare both two-dimensional (2D) and three-dimensional (3D) frontomaxillary facial angle (FMFA) in first trimester, and (ii) to assess the ease with which both may be performed. MATERIALS AND METHODS: Both 3D volumes of the fetal head and 2D fetal profiles were collected from 251 consenting patients during routine first-trimester nuchal translucency (NT) screening. The FMFA in 2D was measured at the time of the NT screening. The 3D FMFA was measured offline. RESULTS: The 2D FMFA was systematically higher than the 3D FMFA. The difference in 3D-2D FMFA was statistically significant from 11+0 to 12+3 weeks. From 12+4 to 13+6 weeks the difference was no longer significant with p = 0.06. Performing the measurement did not unduly increase the time of the study. Even for the experienced sonographer the technique is technically difficult, relying on many factors for accurate caliper placement. DISCUSSION: The 2D FMFA is greater than the 3D angle. This was found in previous studies, but not thought to be statistically significant. The difference decreased with increasing gestational age. There is a learning curve associated with performing this measurement. Normative data for both 2D and 3D, incorporating ethnicity, may be necessary before inclusion in the first-trimester algorithm.
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