Nomograms for the sonographic measurement of the fetal philtrum and chin

Objective: To generate nomograms for the sonographic measurement of the fetal philtrum and chin during pregnancy. Design: A prospective, cross-sectional study in normal singleton pregnancies. Subjects: One hundred and fifty-three fetuses between 13 and 42 weeks of gestation were studied. Methods: The philtrum was measured from the base of the columella to the upper lip. The chin was measured from the tip of the lower lip to the skin under the lower tip of the mandible. Predictive models were evaluated to generate graphic description of the 5th, 50th and 95th centiles for the fetal philtrum and chin. Results: Fetal philtrum length increased with gestational age. The regression equation for the philtrum length (y) according to gestational age in weeks (x) is best predicted by the S-curve (Gompertz) model, as described by the following equation: y = exp(a + b/x), where a = 2.778577, and b = -23.476723 (R² = 85.3%, p < 0.0001). The fetal chin length increased with gestational age. The regression equation for the mean chin length (y) according to gestational age in weeks (x) is best predicted by the S-curve model as described in the following equation, y = exp(a + b/x), where a = 3.7922, b = -28.043, (R² = 89.0%, p < 0.0001). Conclusions: The nomograms generated in this study for the fetal philtrum and chin during pregnancy can be used in confirming subjective impression of facial dysmorphism.