Three-dimensional sonographic determination of normal fetal mandibular and maxillary size during the second half of pregnancy.

Abstract

To explore the various ways of obtaining fetal maxillary and mandibular size with three-dimensional (3D) ultrasound, with a view to developing a tool for identifying minor anomalies in the lower facial region. Serial 3D sonographic measurements of the fetal jaws were made in 126 normal singleton pregnancies at 18-34 weeks of gestation for determination of degree of maxillary and mandibular protrusion, maxillary and mandibular corpus lengths, mid- and lower facial depths and maxillary and mandibular curvature. In a sub study the reproducibility of the measurements was evaluated. The coefficient of variation in the reproducibility study varied between 7.1 and 10.5%. For all parameters except maxillary and mandibular protrusion, there was a significant gestational age-related increase. Ratios of maxillary/mandibular protrusion, maxillary/mandibular corpus lengths, mid-/lower facial depths and maxillary/mandibular curvature all showed a significant gestational age-related decrease, with the most distinct decrease in the mid-/lower facial depth ratio. 3D sonographic measurement of the fetal maxilla and mandible demonstrated an acceptable intraobserver variability for all measurements. The mid-/lower facial depth ratio appears to be most valuable in determining abnormal mandibular development.