Does maternal gastric bypass surgery improve birth outcomes?

A recent research letter appearing in JAMA described a nationwide matched cohort study to investigate major birth defect risk in infants born to women after gastric bypass surgery vs infants born to comparable women without bariatric surgery. Higher maternal body mass index (BMI) and glucose control medications are associated with offspring birth defects, but bariatric surgery to lower weight and BMI is associated with nutritional deficiencies and substance abuse, which can also lead to birth defects. 

The study identified live-born singleton infants in the Swedish Medical Birth Register born in 2007 to 2014. The authors also used the Register to identify the mothers of the infants and then classified them into two groups: those who received Roux-en-Y gastric bypass surgery during that same period and those who did not undergo bariatric surgery. Controls were matched by major birth defects in previous pregnancies, presurgery BMI, and diabetes (early-pregnancy BMI and preconception diabetes used for controls), delivery year, and a propensity score (estimated using logistic regression) including maternal age, smoking alcohol substance use, parity, psychiatric drugs, and number of prescription drugs. The authors identified major birth defects using the National Patient Register and Causes of Death Register through 2015. 

The authors matched controls for 97.4% (2921/2998) of postsurgery-born infants. In the surgery groups, mean presurgery BMI was 43.5 and mean body weight was 122 kg. Median surgery-to-conception interval was 1.6 years and mean weight loss was 40 kg, which resulted in a body weight of 82 kg. Diabetes drug use decreased from 9.7% before surgery to 1.5% during the 6 months before conception.

Major birth defects were recorded in 3.4% (98/2921) of infants born to mothers with gastric bypass surgery vs 4.9% (1510/30573) of controls (RR, 0.67 [95% CI, 0.52-0.87]; risk difference, -1.6% [95% CI, -2.7% to -0.6%]). Major heart defects accounted for 60% (n=58) of birth defects among post-surgery-born infants. There were no cases of neural tube defects in the surgery group and 20 cases (0.07%) among controls.

According to the results of the study, infants born to women with Roux-en-Y gastric bypass surgery had a lower risk to major birth defects than infants born to matched controls. Following bariatric surgery, women lost weight and diabetes drug use diminished, which the authors believe may be the primary contributors to the reduced birth defects.