Epidemiological Investigation of Sex Differences by Cleft Phenotype and Extent in Cleft Lip and/or Palate: The Cohort Study of 4548 Japanese Patients.

Cleft lip and/or palate (CL/P) shows well-recognized sex differences, with a male predominance in cleft lip (CL) and cleft lip and palate (CLP), and a female predominance in isolated cleft palate (CP). However, how these differences vary according to detailed cleft patterns and extent remains unclear. This retrospective observational study included 4548 patients with CL/P treated at the cleft lip and palate center of Aichi-Gakuin University Dental Hospital between 1989 and 2024. Patients were classified using a detailed cleft pattern system. Sex differences were analyzed according to cleft type, laterality, and anatomical extent (complete vs. incomplete) using Chi-square tests. Overall, CL and CLP showed significant male predominance, whereas CP showed significant female predominance. In CL, males were significantly more frequent in incomplete clefts, while no sex difference was observed in complete clefts regardless of laterality. Cleft lip and alveolus showed no overall sex difference, although right-sided alveolar clefts were more common in males. In CP, females were significantly more prevalent, with a stronger female predominance in hard palate clefts than in soft palate clefts. CLP showed marked male predominance; bilateral clefts and incomplete clefts were more male-dominant than unilateral or complete clefts. Sex differences in CL/P vary substantially according to cleft type, detailed pattern, and extent. Male predominance is more evident in less severe CL and CLP, whereas female predominance in CP increases with cleft extent, underscoring the importance of detailed cleft classification in epidemiological and clinical analyses.