Dynamic association between breastfeeding and weight retention within the first year postpartum: A trajectory analysis study based on the China multicentre mother-infant cohort

BACKGROUND: Postpartum Weight Retention (PPWR) is a major risk factor for long-term maternal overweight/obesity and cardiometabolic diseases. Breastfeeding is a key modifiable factor for PPWR, but its dynamic impact and time-varying relationship with PPWR remain unclear. OBJECTIVE: To characterize PPWR trajectories, examine time-varying associations of breastfeeding with PPWR/substantial PPWR (SPPWR, ≥5.0 kg), and test whether early breastfeeding predisposition predicts SPPWR. METHODS: This prospective multicentre cohort study was conducted among 779 Chinese mothers enrolled in the Phoenix Study, with follow-ups at 1, 4, 6, and 12 months postpartum. Group-based trajectory modeling (GBTM) identified PPWR trajectories. Breastfeeding was characterized by mode (EBF, Exclusive Breastfeeding; MBF, Mixed Breastfeeding; NBF, No Breastfeeding) and the Cumulative Breastfeeding Index (CBI) integrating intensity and duration at 1, 6, and 12 months. Linear mixed-effects models and logistic regression examined associations with PPWR/SPPWR; multinomial logistic regression evaluated CBI with trajectory membership. RESULTS: Three PPWR trajectories emerged from 714 participants: low retention (26.6%), moderate retention (59.4%), and high retention (14.0%). EBF and a higher CBI correlated with more favorable weight recovery, with its protective effect after childbirth increasing as the breastfeeding period gets longer. Each 1-point increase in CBI was associated with lower odds of being classified into the high retention trajectory (OR= 0.86, 95% CI: 0.76-0.98, P= 0.020) and the moderate retention trajectory (OR= 0.78, 95% CI: 0.65-0.94, P= 0.007) versus the low retention trajectory. Separately, 'Low Breastfeeding Predisposition/State Class' from Latent Class Analysis (LCA) was associated with a higher risk of SPPWR at 6 months postpartum (OR= 0.60, 95% CI: 0.40-0.90, P= 0.015). CONCLUSION: Early exclusive breastfeeding and greater cumulative breastfeeding exposure were strongly associated with favorable maternal weight trajectories. Low early breastfeeding predisposition/state highlighted an early intervention window for SPPWR. The CBI may serve as a preliminary cumulative exposure indicator in this Chinese cohort.