OBJECTIVE: To assess obstetrical and neonatal outcomes in women following gastric bypass, compared with adipose women without surgery and with a normal weight control population.

DESIGN: Historical controlled cohort study.

SETTING: Denmark.

POPULATION: All women undergoing gastric bypass during the period 1996-2011, and subsequently giving birth.

METHODS AND MAIN OUTCOME MEASURES: Obstetrical and neonatal outcomes in women without gastric bypass matched on age, parity, plurality, year, and body mass index, and normal weight women.

RESULTS: In 415 women giving birth after gastric bypass we found significantly more women with hypertension in pregnancy; relative risk (RR) 2.5 (95% confidence interval 1.3-5.0), gestational diabetes; RR = 6.9 (3.5-13.5), and acute abdominal pain during pregnancy; RR = 4.7 (2.9-7.8) compared with normal weight controls. Compared with women with similar body mass index, they had a lower incidence of preeclampsia and emergency cesarean sections, and their children a lower incidence of asphyxia; RR = 0.4 (0.2-0.8). Their children were on average 212 g smaller than newborn of normal weight mothers, and 319 g smaller than newborn of adipose controls, and had significantly more admissions to neonatal intensive care unit compared with newborn of normal weight mothers; RR = 1.5 (1.1-2.0).

CONCLUSIONS: Gastric bypass may reduce the risk of preeclampsia, emergency cesarean section, and perinatal asphyxia, compared with adipose women without surgery. Compared with normal weight controls women who had had a gastric bypass had a higher risk of hypertension, gestational diabetes, and acute abdominal pain during pregnancy and their children a lower birthweight and higher incidence of admittance to neonatal intensive care.