Obesity during pregnancy associated with increased risk of birth defects

Feb 10 2009

For women who are obese during pregnancy there is an associated increased risk of certain birth defects, such as spina bifida and neural tube defects, although the absolute increase in risk is likely to be small, according to an analysis of previous studies, reported in the February 11 issue of JAMA.

Obesity is a major public health and economic concern. In the United States, a third of women age 15 years and older were obese (body mass index [BMI] greater than 30) in 2004. There are significant health implications of prepregnancy maternal obesity for both mother and child. There is evidence that suggests that maternal obesity may be associated with the development of some congenital anomalies (abnormality present at birth). Congenital anomalies are a leading cause of stillbirth and infant death, accounting for 1 in 5 infant deaths in the United States, and are important contributors to preterm birth and childhood illnesses, according to background information in the article.

Katherine J. Stothard, Ph.D., and colleagues from Newcastle University, Newcastle upon Tyne, U.K., conducted a review and meta-analysis of studies to assess the relationship between maternal overweight and obesity and the risk of congenital anomaly in newborns. The researchers identified 39 articles that were included in a systematic review and 18 articles in the meta-analysis.

"In women who were obese at the start of pregnancy, the meta-analysis demonstrated a significantly increased risk of a pregnancy affected by a neural tube defect [nearly twice the odds], including spina bifida [more than twice the odds]; cardiovascular anomaly, including a septal anomaly [heart defect]; cleft palate and cleft lip and palate; anorectal atresia [abnormality of the anus/rectum]; hydrocephaly [abnormal enlargement of the ventricles of the brain due to accumulation of cerebrospinal fluid]; and a limb reduction anomaly," the authors write.

The risk of gastroschisis (abdominal wall defect) among obese mothers was significantly reduced.

"An estimated 3 percent of all livebirths in the United States are affected by a structural anomaly with 0.68 per 1,000 births being affected by a neural tube defect and 2.25 per 1,000 births being affected by a serious heart anomaly. Given the findings of this review, and the BMI profile of the female population during the period when these estimates were generated, we calculate that the absolute risk of a pregnancy affected by a neural tube defect or a serious heart anomaly is respectively 0.47 per 1,000 births and 0.61 per 1,000 births greater in an obese woman than a woman of recommended BMI in prepregnancy or early pregnancy. This has health implications, particularly given the continued rise in the prevalence of obesity in many countries," the authors write.

They add that further studies are needed to confirm whether maternal overweight is also implicated.