Frontomaxillary facial angle at 11+ 0 to 13+ 6 weeks: effect of plane of acquisition

Objective To determine the range of positions of the fetal head in which a three-dimensional (3D) volume is acquired for subsequent successful assessment of the frontomaxillary facial (FMF) angle. Method We obtained 3D volumes of the fetal head at 11 + 0 to 13 + 6 weeks. The volumes were acquired with the head in different positions and reconstructed to obtain a mid-sagittal section and demonstrate the maxilla, palate and frontal bone, which constitute the landmarks for the assessment of the FMF angle. Results In the reconstructed mid-sagittal sections, it was possible to demonstrate the landmarks that define the FMF angle in most of the cases when the 3D volume acquisition plane was: (a) mid-sagittal, with the angle between the face of the transducer and the direction of the fetal nose being about 0–99◦, 150–199 ◦ and 330–359◦; (b) transverse at the level of the biparietal diameter when the angle between the transducer and the midline echo of the brain was 0–29◦; and (c) oblique around the crown–rump axis when the angle from the mid-sagittal plane was 0–49◦. However, the measurement of the FMF angle was artificially increased when in the mid-sagittal plane the angle was 40–99 ◦ and 150–199◦. Conclusion Successful assessment of the FMF angle by 3D ultrasound is dependent on the plane and angle of the volume acquisition. Copyright 2007 ISUOG. Publishe