A Novel Fetal Intracranial Measurement Contributing to the Differential Diagnosis of Fetal Microcephaly

OBJECTIVES: To evaluate the value of the thickness of the frontal lobe (TFL) and foramen magnum-to-cranium distance (FCD) for predicting poor neurodevelopmental outcomes in fetuses with a small head circumference (HC). METHODS: This retrospective observational study included 39 fetuses with HC < -2 standard deviations (SD) and 592 prospectively collected controls with normal growth. TFL was defined as the shortest distance between the upper outer border of the corpus callosum and the upper inner cranial border parallel to the FCD. Reference ranges for FCD and TFL were established in 592 healthy fetuses between 21 and 38 weeks of gestation and applied to fetuses with suspected microcephaly. Diagnostic performance was assessed using sensitivity, specificity, and SD-based thresholds. RESULTS: Normal reference ranges for FCD and TFL across gestation were established. All fetuses with normal postnatal outcomes had TFL values within the normal range, whereas reduced TFL was observed only in fetuses with poor neurodevelopmental outcomes. For predicting adverse outcomes, TFL