To the Editor In a Research Letter, Dr Neovius and colleagues investigated the association between gastric bypass surgery and risk of birth defects in offspring.1 The authors found that bariatric surgery was protective against birth defects.
Although the data set was large, the results are somewhat challenging to interpret because of the choice of comparison group. The authors identified 2921 pregnant women with previous gastric bypass surgery and a comparison group of pregnant women with no history of bypass surgery. Women were matched on several risk factors for birth defects, including weight and diabetes. However, the authors matched the presurgery body mass index (BMI) for exposed women with the BMI at the time of pregnancy for controls. Similarly, women who had diabetes before surgery were matched with controls who had diabetes during pregnancy. Because women were less obese and had better glucose control after gastric bypass surgery, the authors compared women who lost weight after surgery with women who were more obese and had diabetes. Obesity and diabetes are both risk factors for birth defects;2 thus, it is expected that women who lose weight after bariatric surgery will have a lower risk of birth defects. The results confirm that weight loss is an effective tool to reduce the risk of birth defects but do not answer the question of whether women with gastric bypass procedures have an elevated risk of birth defects relative to women with similar weight.
Auger N, Bilodeau-Bertrand M, Arbour L. Risk of Offspring Birth Defects in Women After Bariatric Surgery. JAMA. 2020;323(7):668. doi:10.1001/jama.2019.20977
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