Association between time interval from bariatric surgery to pregnancy and maternal weight outcomes

Background: The majority of patients having bariatric surgery are reproductive-age women who are advised to delay pregnancy for at least 12 months after surgery. Many women become pregnant sooner and the association between gestational weight gain (GWG) and maternal long-term weight is unknown. Objectives: The primary objective of this study was to compare weight outcomes in pregnancies occurring < 12 months versus >= 12 months after bariatric surgery. The secondary objectives were to determine the association between time interval from bariatric surgery to pregnancy and maternal nutritional status and maternal and neonatal outcomes. Study design: This is a retrospective cohort study of women with singleton livebirths after bariatric surgery who received care at a single tertiary care center between 2009 and 2017. GWG was the difference in weight between the first prenatal visit and delivery. GWG adequacy was determined by the IOM 2009 guidelines according to prepregnancy BMI (inadequate, adequate, excessive). Postpartum weight retention was calculated as the difference between weight at first prenatal visit and measured postpartum weight. Weight outcomes along with maternal nutritional status and maternal and neonatal outcomes were compared between < 12 months versus >= 12 months after bariatric surgery with t-tests, Mann-Whitney U and chi-square tests, as appropriate. Results: Of the 76 pregnancies that met inclusion criteria, 36.8% occurred < 12 months (median 7.2 months) and 63.2% occurred >= 12 months after surgery (median 26.9 months). Of those with pregnancies < 12 months from surgery, 34% had a restrictive procedure (adjustable gastric band or sleeve gastrectomy) while 66% had a combined restrictive-malabsorptive procedure (Roux-en-Y gastric bypass). In the >= 12 months group, 42.3% had a restrictive procedure while 57.7% had a combined restrictive-malabsorptive procedure. There were no significant differences in maternal age, ethnicity or nulliparity between groups, but there were more women with obesity in the < 12 months group (75 vs. 52%, p = .03). The mean prepregnancy BMI in the < 12 months group was 34.3 vs. 31.2 kg/m(2) in the >= 12 months group. The < 12 months group had lower mean GWG (4.9 vs. 10.9 kg, p = .01) and higher frequency of weight loss during pregnancy (28.6 vs. 4.2%, p < .01) compared to the >= 12 months group. The < 12 months group had significantly less postpartum weight retention at 6 months compared to the >= 12 months group (-1.3 vs. 8.3 kg, p = .02). The < 12 months group had a higher prevalence of vitamin B12 deficiency (23.1 versus 4.9%, p = .05). There were no differences in hyperemesis, hypertensive disorders, gestational diabetes or delivery mode between groups (p > .05). There were no differences in gestational age at delivery, birth weight and small for gestational age infants between groups (p > .05). Conclusion: Pregnancy < 12 months after bariatric surgery is associated with significantly lower mean GWG and a higher frequency of weight loss during pregnancy as well as less postpartum weight retention at 6 months. Although there were no differences birthweight, weight loss during pregnancy and its accompanying metabolic changes are concerning for a developing fetus. Further study is needed to determine the optimal timing of pregnancy after bariatric surgery with respect to both maternal and infant short and long-term outcomes.