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Prepregnancy body mass index and risk of macrosomia after fresh embryo transfer: a retrospective cohort study with
1Reproductive Medicine Center, Department of Obstetrics and Gynecology, Tangdu Hospital, Fourth Military Medical University, Xi'an, China.
Background:
Higher prepregnancy body mass index (BMI) is a well-established risk factor for adverse neonatal outcomes in IVF-conceived pregnancies; therefore, weight management is important for infertile patients, yet it remains challenging. Determining a clinically applicable BMI threshold for neonatal outcome risk assessment in fresh embryo transfer (fresh ET) cycles is meaningful; however, it remains undetermined. Therefore, this study aimed to identify an exploratory BMI threshold associated with increased risk of adverse neonatal outcomes after fresh ET, providing a preliminary reference for clinical risk communication.
Methods:
This retrospective cohort study included 2,195 women who underwent autologous fresh ET between June 2019 and December 2023. Multivariable regression analysis examined the association between prepregnancy BMI and neonatal outcomes. Smooth curve fitting and threshold effect analysis identified the exploratory BMI threshold. Adjusted analysis following propensity score matching (PSM) was conducted as a sensitivity analysis to validate the robustness of the results.
Results:
The multivariate regression analyses revealed that birthweight (adjusted β: 22.63, 95% CI: 14.53 to 30.73; P<0.001) and Z-score (adjusted β: 0.06, 95% CI: 0.04 to 0.08; P<0.001) were positively associated with increasing maternal BMI. Compared with the reference group (BMI 18.5-24.9 kg/m²), the incidence of macrosomia was increased by 2.25-fold in the BMI 25-29.9 kg/m² group (adjusted OR: 2.25, 95% CI: 1.29 to 3.93; P = 0.004) and by 4.56-fold in the BMI ≥30 kg/m² group (adjusted OR: 4.56, 95% CI: 2.26 to 9.22; P<0.001). Smooth curve fitting and threshold effect analysis revealed a significant increase in the odds of macrosomia when BMI exceeded 26.22 kg/m² (adjusted OR: 4.05, 95% CI: 2.47 to 7.29; P = 0.0009). PSM analysis confirmed that patients with a BMI >26.22 kg/m² (adjusted OR: 3.01, 95% CI: 2.02 to 4.47; P<0.001) had significantly higher odds of macrosomia compared to those with BMI ≤26.22 kg/m².
Conclusion:
Our findings suggest that a prepregnancy BMI exceeding approximately 26 kg/m² may be a potential predictor for an increased risk of macrosomia in singleton pregnancies conceived via fresh ET. This exploratory threshold may serve as a preliminary reference for risk communication and weight management counseling in women undergoing IVF treatment, though external validation is needed.
