Two-Dimensional Characterization of Maternal BMI and Height Associations With Pregnancy and Perinatal Outcomes After Frozen Embryo Transfer.

AIM: To characterize maternal body mass index (BMI) and height as two nearly independent body-size dimensions in relation to pregnancy and perinatal outcomes after frozen-thawed embryo transfer (FET), and assess whether their joint evaluation reveals patterns not captured by BMI alone. METHODS: In a single-center retrospective cohort of 10 059 FET cycles, dose-response relationships of BMI and height with 15 pregnancy-related outcomes were modeled using restricted cubic splines with modified Poisson regression and robust variance estimators. A joint additive model generated two-dimensional risk surfaces adjusted for maternal age, endometrial preparation, and obstetric covariates. RESULTS: BMI was significantly associated with nine of 15 outcomes and height with seven. Two-dimensional risk maps showed outcome-specific patterns: hypertensive disorders of pregnancy were predominantly BMI-associated, whereas small-for-gestational-age and gestational diabetes reflected both dimensions, with higher risks in the low-BMI/short-stature and high-BMI/short-stature regions, respectively. Exploratory subgroup analyses by endometrial preparation method suggested possible heterogeneity for cesarean section, large-for-gestational-age, and miscarriage. CONCLUSIONS: Joint evaluation of BMI and height revealed heterogeneous body-size risk patterns-predominantly BMI-associated, height-associated, or combined-that BMI alone does not capture. Because height is readily available before pregnancy, considering it with BMI may refine body-size risk assessment after FET.