Gestational weight gain trajectories and adverse pregnancy outcomes: effect modification by pre-pregnancy BMI

Abstract Background The increasing prevalence of obesity and excessive gestational weight gain (GWG) highlights the need to clarify their independent and joint associations with adverse pregnancy outcomes (APOs). Methods A prospective cohort study enrolled 1125 pregnant women at Qingdao Women & Children’s Hospital (March–December 2023). GWG trajectories were identified using group-based trajectory modelling. Binomial logistic regression assessed associations between pre-pregnancy BMI (ppBMI), GWG trajectories, and APOs, adjusting for 13 covariates across three models. Stratified analyses examined effect modification by ppBMI. Outcomes included cesarean delivery (CD), preterm birth, low birth weight (LBW), macrosomia, small for gestational age (SGA), large for gestational age (LGA), gestational diabetes mellitus (GDM), gestational hypertension (GHp), and preeclampsia. Results Among 833 participants, four GWG trajectories were identified: slow (6.4%), moderate (45.0%), fast (39.5%), and extremely fast (9.1%). Pre-pregnancy overweight/obesity was independently associated with higher risks of CD, GDM, preeclampsia, macrosomia, and LGA (adjusted odds ratios [aORs] 1.72–3.87). For GHp, unadjusted analysis suggested an elevated risk in overweight/obese women (OR 3.28, Peto OR 5.09, 95% CI 1.84–14.10), but the low event rate (2.6%) precluded multivariable adjustment. No associations were observed for preterm birth, LBW, or SGA (Peto estimates consistent with crude estimates). Accelerated GWG trajectories (fast and extremely fast) were independently associated with increased risks of macrosomia and LGA (fast: aOR 2.52 and 2.03; extremely fast: aOR 7.51 and 4.85, respectively), and the extremely fast trajectory was also associated with CD (aOR 2.04). Stratified analyses revealed that the adverse associations of accelerated GWG on macrosomia and LGA were confined to women with normal pre-pregnancy weight, with no significant associations observed among overweight/obese women. Conclusions Pre-pregnancy overweight/obesity was independently associated with multiple APOs. Accelerated GWG trajectories were also independently linked to increased risks of fetal overgrowth and cesarean delivery. Crucially, stratified analyses revealed that rapid weight gain was associated with substantial risks only among normal-weight women, although the interaction tests were not statistically significant. These findings may support a stratified approach to weight management based on ppBMI status.