Maxilla–nasion–mandible (MNM) angle: an indicator to assess fetal facial profile in first-trimester of pregnancy

Objective The aim of this study was to observe whether there existed significant differences in the maxilla–nasion–mandible angle (MNM) between the first- and second-trimester of pregnancy, and to observe its predictive values for trisomy 18. Methods Two experienced ultrasonologists used 2D and 3D ultrasound imaging techniques to obtain the facial sagittal sections of fetuses in the first-trimester of pregnancy (crown-rump length 45–84 mm), respectively, so as to measure MNM. Results MNM could be measured in 91 % of normal fetuses, and the measurement differences by different operators in different groups were