Ultrasonographic study of fetal mandibular markers during the first trimester in a Chinese population

To establish reference ranges for fetal mandibular markers in low-risk singleton pregnancies between 11 and 13 + 6 weeks of gestation in a Chinese population.

The inferior facial angle (IFA), transverse, and anteroposterior diameters of the mandible, and mandibular length were measured at 11-13 + 6 weeks of gestation. The utility of these sonographic markers for detecting micrognathia was explored in seven fetuses.

In healthy fetuses at 11-13 + 6 weeks, there were linear correlations between gestational age and the transverse (Y = -15.615 + 1.987X, r = 0.718, p < 0.001) and anteroposterior (Y = -8.557 + 1.101X, r = 0.581, p < 0.001) diameters of the mandible; mean ratio of the anteroposterior: transverse diameters of the mandible decreased with gestational age (Y = 0.603-0.003X, r = 0.018, p = 0.755); there was a positive correlation between crown rump length and mandibular length (mandible length = 0.861 + 0.137*crown rump length; r = 0.723, p < 0.001); and there was a positive correlation between crown rump length and IFA (r = 0.234, p < 0.05). Reference ranges were: mean ratio of anteroposterior diameter: transverse diameter of the mandible 0.56; mean mandibular length 9.05 mm; and median IFA 66.5°. The values for these mandibular markers in seven cases of fetal micrognathia were outside the normal range.

Evaluations of fetal mandibular markers during first trimester ultrasound screening may contribute to the early detection and diagnosis of micrognathia. We recommend obtaining a subjective impression of the mandible on the mid-sagittal view routinely used to measured nuchal translucency, followed by targeted objective measurements on the mid-sagittal and axial views in suspected cases.