Reassessing Parity-Related Variation in Female Body Morphology: A Matched Analysis in a Contemporary Population

Morphological differences between parous and nulliparous women have long been interpreted as reproductive signatures. However, such patterns may instead reflect demographic composition. This study aimed to reassess parity-related morphological variation by reducing confounding from age and BMI using propensity score matching (PSM).

Anthropometric data from 1339 Korean women aged 20-39 years were analyzed. Forty-five direct and derived body dimensions, collected following ISO 7250-1:2017, were compared between parous and nulliparous women before and after 1:1 nearest-neighbor PSM on age and BMI. Group differences were examined for torso breadths, depths, circumferences, and proportional indices.

Unadjusted analyses reproduced well-known findings: parous women showed greater abdominal breadths and depths, larger circumferences, and adiposity patterns commonly attributed to childbirth. After PSM, however, most differences-including widely cited markers of lower-body enlargement and postpartum contour change-were substantially attenuated or statistically nonsignificant. Only a small number of proportional indices (e.g., underbust/weight, waist/weight, elbow/weight) retained modest differences, indicating that parity leaves limited, anatomically localized morphological signatures rather than broad structural changes.

Demographic composition, rather than reproductive biology alone, accounts for much of the observed variation in cross-sectional datasets. Matching-based approaches clarify the independent contribution of parity, strengthen causal inference in anthropometric research, and underscore the need to consider population structure when interpreting life-history-related variation in adult female morphology.