Prenatal Exome Sequencing for Fetal Macrocephaly: A Large Prospective Observational Cohort Study

ABSTRACT Objective To assess the diagnostic utility of exome sequencing (ES) in macrocephalic fetuses. Methods Fetuses with macrocephaly (head circumference (HC) ≥ +2 SD) and negative chromosomal microarray results were included, who had available trio‐ES data. Molecular diagnoses were systematically analyzed. Subgroup analyses were performed on the ES diagnostic yield based on gestational age, HC Z ‐scores, associated anomalies, and growth parameters. Results Molecular diagnoses were established in 34 out of 87 macrocephalic fetuses (39.1%) through trio‐ES. These diagnoses revealed that the variants predominantly affect key signaling pathways, including mTOR, RASopathies and Sotos syndrome. The detection rate was significantly higher in non‐isolated compared to isolated macrocephaly cases (65.0%, 26/40 vs. 17.0%, 8/47; p < 0.001). The most frequent anomalies associated with genetic diagnoses included micromelia (100.0%, 14/14), megalencephaly (100.0%, 2/2), and ventriculomegaly (60.0%, 6/10). Subgroup analysis identified higher diagnostic yields in fetuses diagnosed before 32 gestational weeks, with HC Z ‐scores ≥ +3 SD, micromelia, and absence of large‐for‐gestational‐age (LGA). Conclusions Exome sequencing significantly enhances the detection of monogenic disorders in macrocephalic fetuses compared with CMA, irrespective of isolated or non‐isolated cases. These clinical features and phenotypes are essential for assessing monogenic disorders and for prenatal counseling and evaluations of macrocephalic fetuses.