The fetal mandible: an in utero sonographic evaluation between 11 and 31 weeks' gestation

OBJECTIVE: To construct a growth chart of the mandible throughout gestation. METHODS: A prospective cross-sectional study of normal singleton pregnancies was conducted. Measurements of the fetal mandibular transverse and antero-posterior diameters were performed with high-resolution transvaginal and transabdominal ultrasonography in 490 pregnant women with singleton low-risk pregnancies between 11 and 31 weeks' gestation. RESULTS: The mandibular transverse and antero-posterior diameters were recorded by week of gestation and the ratio was calculated: mandibular ratio (MR) = 1.7759 - 0.01047 x gestational week. There was a negative linear correlation (-1.047%) for each incoming week of gestation. Normal values (+/-1SD and 2SD) were established. CONCLUSION: The present data provides a normal range of fetal mandibular diameters during normal pregnancies and introduces a new parameter, the mandibular ratio, for the intrauterine assessment of the fetal mandibular development.