Maternal Hypoglycemia and Reduced Foetal Growth in Pregnancies Following Roux‐en‐Y Gastric Bypass: A Prospective Cohort Study

INTRODUCTION: The risk of delivering a small-for-gestational-age (SGA) neonate is increased after Roux-en-Y gastric bypass (RYGB). Because glucose is the foetus's primary energy source and postprandial hypoglycemia is common after RYGB, the Bariatric surgery And consequences for Mother and Baby In pregnancy (BAMBI) study examined associations between trimester specific maternal hypoglycemia and offspring birthweight as well as other perinatal outcomes. MATERIALS AND METHODS: Twenty-three pregnant women with RYGB and 23 BMI- and parity-matched controls were followed prospectively with continuous glucose monitoring (CGM) and foetal ultrasounds in each trimester. At birth, neonatal anthropometric measures, including skinfold measurements, were obtained. Exposure to hypoglycaemia was defined as spending > 4% of the time with interstitial glucose < 3.5 mmol/L. Multivariable regression was used to examine associations between exposure to hypoglycaemia in each trimester and birthweight, adjusting for maternal age, parity, pre-pregnancy body mass index, gestational weight gain and surgery-to-conception interval. RESULTS: Baseline characteristics were similar regardless of exposure to hypoglycemia. Spending > 4% of the time in hypoglycemia during the second or third trimester was associated with a 550 g lower birthweight (95% CI [-1031--69], p = 0.03), while no such association was observed for the first trimester. Infants exposed to second/third trimester hypoglycemia had lower abdominal circumference percentiles (20th vs. 55th, p = 0.01) and lighter placentas (580 g vs. 705 g, p = 0.01). CONCLUSION: Increased maternal hypoglycemia in the second or third trimester of pregnancy post-RYGB appears to be associated with reduced foetal growth. Optimising glucose levels through CGM may help prevent SGA births in this population. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT03713060.