Obesity during pregnancy increases the risk of birth defects

A new study published in the February 11 issue of JAMA found that pregnant mothers who were overweight or obese had an  increased risk of having a baby with congenital abnormalities.

In New Zealand, one in three adults is overweight and a further one in four is obese. Obesity is a major public health concern and there are significant health implications both for mothers who are obese and for their infants. During pregnancy, obesity increases the risk of gestational diabetes, hypertensive disorders and cesarean delivery in the mother, and infants of obese mothers are at increased risk of birth difficulties, macrosomia and perinatal death.

This latest study, by Katherine Stothard and colleagues from Newcastle University, involved a systematic review and meta-analysis of observational studies to assess and quantify the relationship between maternal overweight and obesity and the risk of a congenital abnormality in the offspring. Obese mothers were at significantly increased odds of a pregnancy affected by a neural tube defect and by anencephaly compared with mothers of recommended BMI. There was a 2-fold increased odds of a pregnancy affected by spina bifida in obese mothers compared with mothers of a recommended BMI.

The authors calculated that the absolute risk of a pregnancy affected by a neural tube defect or a serious heart anomaly is respectively 0.47 per 1000 births or 0.61 per 1000 births greater in an obese woman than in a women of recommended BMI in pre-pregnancy or early pregnancy.

Although maternal obesity is associated with an increased risk of a range of structural anomalies the absolute risk is likely to be small. Further studies are needed to confirm whether maternal overweight is also implicated.

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