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.

致编辑在一封研究信函中，Neovius 博士及其同事调查了胃绕道手术与后代出生缺陷风险之间的关联。¹作者发现，减肥手术可以预防出生缺陷。

尽管数据集很大，但由于比较组的选择，结果难以解释。作者确定了 2921 名既往接受过胃绕道手术的孕妇和一个没有胃绕道手术史的孕妇对照组。女性在出生缺陷的几个风险因素上进行了匹配，包括体重和糖尿病。然而，作者将暴露女性的术前体重指数 (BMI) 与怀孕时的 BMI 进行了对比。同样，手术前患有糖尿病的女性与怀孕期间患有糖尿病的对照组相匹配。由于女性在胃绕道手术后体重较轻且血糖控制较好，因此作者将手术后体重减轻的女性与较肥胖且患有糖尿病的女性进行了比较。²因此，预计减肥手术后体重减轻的女性出生缺陷的风险较低。结果证实，减肥是降低出生缺陷风险的有效工具，但没有回答接受胃绕道手术的女性相对于体重相似的女性是否具有更高的出生缺陷风险的问题。