Preconception maternal gastric bypass surgery and the impact on fetal growth parameters.

Background: Bariatric surgery is increasingly performed in women of reproductive age. As bariatric surgery will result in postoperative rapid catabolic weight loss which potentially leads to fetal malnutrition and directly related impaired intra-uterine growth, it is advised to postpone pregnancy for at least 12-18 months after surgery.

Objectives: To investigate the consequences of preconception gastric bypass surgery (pGB) on fetal growth parameters and maternal pregnancy outcome.

Setting: Maasstad Hospital, The Netherlands, general hospital and Erasmus Medical Center, The Netherlands, university hospital.

Methods: We included 97 pGB pregnancies (Maasstad hospital) and 440 non-bariatric pregnancies (Rotterdam Periconception cohort, Erasmus Medical Center). Longitudinal second and third trimester fetal growth parameters (head circumference, biparietal diameter, femur length, abdominal circumference, estimated fetal weight) were analyzed using linear mixed models, adjusting for covariates and possible confounders. Fetal growth and birthweight in pGB pregnancies were compared to non-bariatric pregnancies and Dutch reference curves. Maternal pregnancy outcome in the pGB group was compared to non-bariatric pregnancies.

Results: All fetal growth parameters of pGB pregnancies were significantly decreased at 20 weeks' gestation (P < .001) and throughout the remaining part of pregnancy (P < .05) compared with non-bariatric pregnancies (crude and adjusted models). In our cohort, gestational weight gain was not significantly associated with birthweight corrected for gestational age. Birthweight was significantly lower in pGB pregnancies (estimate -241 grams [95% CI, -342.7 to -140.0]) with a 2-fold increased risk of small-for-gestational-age (SGA) (adjusted odds ratio 2.053 [95% CI, 1.058 to 3.872]). Compared to the non-bariatric pregnancies, we found no significant differences in maternal pregnancy outcome.

Conclusions: PGB is associated with overall reduced fetal growth trajectories and a 2-fold increased risk of SGA, without significant adverse consequences for maternal pregnancy outcome. We recommend close monitoring of fetal growth after pGB.