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During pregnancy, being overweight (body-mass index, 25–30 kg/m2) or obese (BMI, >30) confers substantial risks for both mother and child for several conditions, including gestational diabetes, hypertension, operative delivery, macrosomia, and birth trauma. U.K. investigators examined specific risk for congenital anomalies in a meta-analysis of 18 studies (published from 1966–2008).
Compared with women at recommended BMIs, obese women delivered infants with higher risk for several congenital anomalies, including spina bifida (odds ratio, 2.24), neural-tube defects (OR, 1.87), hydrocephaly (1.68), anorectal atresia (1.48), limb reduction anomalies (1.34), cardiovascular anomalies (1.30), and cleft palate (1.23). The ORs associated with overweight mothers compared with those of mothers at recommended BMIs were somewhat smaller but still significantly elevated for neural-tube defects (1.20) and cardiovascular anomalies (1.17) and nonsignificantly elevated for the other anomalies.
Stothard KJ et al. Maternal overweight and obesity and the risk of congenital anomalies: A systematic review and meta-analysis. JAMA 2009 Feb 11; 301:636.
Comment
The authors propose several potential mechanisms for this excess risk, including insulin resistance and hyperglycemia, but they point particularly to folic acid deficiency. Obesity is associated with reduced folate levels, and several of these anomalies occur at nearly the same time in development. Risk for marked structural anomaly in all pregnancies is roughly 3%, so these odds ratios are not clinically unimportant and provide yet one more reason to encourage prevention of obesity or to treat it in women before they become pregnant.