Pre-pregnancy body mass index and risk of maternal or infant complications with gestational diabetes mellitus as a mediator: A multicenter, longitudinal cohort study in China

Aims We explored the complex relationships between pre-pregnancy body mass index (pBMI) and maternal or infant complications and the mediating role of gestational diabetes mellitus (GDM) in these relationships. Methods Pregnant women from 24 hospitals in 15 different provinces of China were enrolled in 2017 and followed through 2018. Propensity score–based inverse probability of treatment weighting, logistic regression, restricted cubic spline models, and causal mediation analysis were utilized. In addition, the E-value method was used to evaluate unmeasured confounding factors. Results A total of 6174 pregnant women were finally included. Compared to women with a normal pBMI, obese women had a higher risk for gestational hypertension (odds ratio [OR] = 5.38, 95% confidence interval [CI]: 3.48–8.34), macrosomia (OR = 2.65, 95% CI: 1.83–3.84), and large for gestational age (OR = 2.05, 95% CI: 1.45–2.88); 4.73% (95% CI: 0.57%-8.88%), 4.61% (95% CI: 0.51%-9.74%), and 5.02% (95% CI: 0.13%-10.18%) of the associations, respectively, were mediated by GDM. Underweight women had a high risk for low birth weight (OR = 1.42, 95% CI: 1.15–2.08) and small for gestational age (OR = 1.62, 95% CI: 1.23–2.11). Dose–response analyses indicated that 21.0 kg/m2 may be the appropriate tipping point pBMI for risk for maternal or infant complications in Chinese women. Conclusion A high or low pBMI is associated with the risk for maternal or infant complications and partly mediated by GDM. A lower pBMI cutoff of 21 kg/m2 may be appropriate for risk for maternal or infant complications in pregnant Chinese women.