Intentional gestational weight loss among women with obesity and fetal growth: a population-based retrospective cohort study

Abstract Objective The impact of intentional gestational weight loss (GWL) on fetal growth among women with obesity remains unclear. This study aimed to examine the association between women with body mass index (BMI) ≥ 30 kg/m2 who experienced intentional weight loss during pregnancy and the risk of small-for-gestational-age (SGA) and large-for-gestational-age (LGA) neonates. Methods We conducted a retrospective, population-based cohort study of low-risk women with pre-pregnancy obesity resulted in a singleton live birth between 2012–2017, using birth registry data from the Canadian province of Ontario. GWL is defined as negative gestational weight change (≤ 0 kg). Pregnant women with conditions that could cause unintentional weight loss were excluded. Adjusted risk ratio (aRR) and 95% confidence interval (CI) for the association between intentional GWL and fetal growth were estimated using generalized estimating equation models with multiple imputation for missing covariates. Stratified analysis was conducted by obesity class (I:30-34.9 kg/m2, II:35-39.9 kg/m2 and III+:≥40 kg/m2). Results Among 52,184 eligible women who entered pregnancy with a BMI ≥ 30 kg/m2, 5.3% had intentional GWL. Overall, intentional GWL was associated with an increased risk of SGA neonates (aRR:1.50, 95%CI:1.36–1.63) and decreased risk of LGA neonates (aRR:0.80, 95%CI:0.68–0.92), compared to adequate gestational weight gain. Intentional GWL in women who entered pregnancy with obesity was associated with increased risk of SGA neonates regardless of obesity class; however, decreased risk of LGA neonates was associated with intentional GWL only in women with obesity class II or higher category of obesity. Sensitivity analysis with complete case data revealed similar results. Conclusion Intentional GWL in women with obesity was associated with an increased risk of SGA neonates in all obesity classes but was associated with a reduced risk of LGA neonates in women with class II or higher obesity. Recommendations of GWL for women with obesity should be interpreted with caution.