Risk related to gestational weight loss among individuals with obesity: a population-based cohort study.

Objective: There is no clear evidence on the risk of gestational weight loss (GWL) for individuals with obesity. Our study aimed to assess the association between GWL and adverse perinatal outcomes among individuals with obesity.

Methods: This population-based retrospective cohort study examined individuals with prepregnancy BMI ≥ 30 kg/m² who had a singleton pregnancy, using Ontario, Canada, birth registry data from 2012 to 2020. The primary outcome was a composite of adverse outcomes, including perinatal death and neonatal morbidity. The association between GWL and risk of adverse perinatal outcomes was estimated using generalized estimating equation models and restricted cubic spline regression analysis. Stratified analysis was conducted by obesity class.

Results: Of the 157,205 individuals with obesity, 6.1% experienced GWL. Compared with adequate gestational weight gain, GWL was associated with an increased risk of a composite of adverse perinatal outcomes (adjusted risk ratio: 1.31; 95% CI: 1.22-1.39). Similar results were observed in the stratified analysis. Restricted cubic spline regression analysis revealed that average weekly gestational weight changes displayed a nonlinear U-shaped association, with a higher risk of a composite of adverse perinatal outcomes noted in the extremities, particularly toward GWL and excessive weight gain.

Conclusions: Our findings suggest that GWL may increase the risk of adverse perinatal outcomes across all obesity classes.