ImportancePregnancy weight gain may affect the association of bariatric surgery with postsurgery pregnancy outcomes. However, the association of pregnancy weight gain with bariatric surgery is unclear.ObjectiveTo compare pregnancy weight gain among women with a history of bariatric surgery vs those without and to investigate whether pregnancy weight gain differs by surgical procedure, surgery-to-conception interval, and/or surgery-to-conception weight loss.Design, Setting, and ParticipantsThis nationwide, population-based matched cohort study was conducted in Sweden from 2014 to 2021. Singleton pregnancies with a history of bariatric surgery were propensity score matched (1:1) to pregnancies without such a history according to early-pregnancy body mass index (BMI), prepregnancy diabetes, prepregnancy hypertension, maternal age, smoking status, education level, height, country of birth, and delivery year. In addition, post–gastric bypass pregnancies were matched to post–sleeve gastrectomy pregnancies using the same matching strategy. Data analysis was performed from November 2022 to May 2023.ExposureHistory of bariatric surgery.Main Outcomes and MeasuresPregnancy weight gain was standardized by gestational age into early-pregnancy BMI-specific z scores.ResultsThis study included 12 776 pregnancies, of which 6388 had a history of bariatric surgery and 6388 were matched controls. The mean (SD) age was 31.6 (4.9) years for the surgery group and 31.4 (5.2) for the matched controls, with an early-pregnancy mean (SD) BMI of 29.4 (5.2) in both groups. Across all early-pregnancy BMI strata, women with a history of bariatric surgery had lower pregnancy weight gain than matched controls. The differences in pregnancy weight gain z score values between the 2 groups were −0.33 (95% CI, −0.43 to −0.23) for normal weight, −0.33 (95% CI, −0.40 to −0.27) for overweight, −0.21 (95% CI, −0.29 to −0.13) for obese class I, −0.16 (95% CI, −0.29 to −0.03) for obese class II, and −0.08 (95% CI, −0.28 to 0.13) for obese class III. Pregnancy weight gain did not differ by surgical procedure. A shorter surgery-to-conception interval (particularly within 1 year) or lower surgery-to-conception weight loss was associated with lower pregnancy weight gain.Conclusions and RelevanceIn this nationwide matched cohort study, women with a history of bariatric surgery had lower pregnancy weight gain than matched controls with similar early-pregnancy characteristics. Pregnancy weight gain was lower in those with a shorter surgery-to-conception interval or lower surgery-to-conception weight loss, but did not differ by surgical procedure.
