Sex Determination Using Image Processing Reveals Elliptical Features of the Female Pelvic Inlet

Abstract

The pelvic inlet is one of the critical constraints within the relatively narrow birth canal for the passage of the fetal head. This study tested the hypothesis that the shape of the pelvic inlet differs between females and males, with the expectation that the female pelvic inlet is more elliptical than its male counterpart. Abdomino-pelvic computed tomography images from 600 cases, equally distributed by sex and age groups, were analyzed. Using 3D reconstruction, image processing, ellipse fitting, and a genetic algorithm, we evaluated whether the proposed measures of elliptical similarity in pelvic inlet shape varied by sex. Additionally, discriminant analysis was employed to assess the accuracy of sex determination based on these measures. The results demonstrated significant differences between the two sex groups for all proposed measures. Discriminant analysis achieved a maximum sex determination accuracy of 79.7%. These findings support the hypothesis that the female pelvic inlet has evolved to be more elliptical compared to the male pelvic inlet. If validated by future studies on diverse populations, this hypothesis may gain broader scientific acceptance. © 2025 Elsevier B.V., All rights reserved.