Study Links Prepregnancy Obesity and Birth Defects (8/11/2007)

In a large multi-site study of obesity and birth defects, epidemiologists at The University of Texas School of Public Health found that women who were obese before they became pregnant had a higher risk of having babies with certain birth defects.

Biological changes due to maternal obesity may (or may not) be the direct cause of these research findings. Other explanations are possible, according to the researchers. Obese women may have differences in the types of food that they eat, the weight loss techniques that they use, or other factors that could influence their risk of having an infant with a birth defect.

Published in the August issue of the Archives of Pediatrics & Adolescent Medicine, a journal of the American Medical Association, the study, "Prepregnancy Obesity as a Risk Factor for Structural Birth Defects," found a significant increase in several types of birth defects, including a defect of the spine, heart defects, limb abnormalities and a gastrointestinal abnormality.

Data for the study was provided by the National Birth Defects Prevention Study (NBDPS), which collected information from mothers of children with and without birth defects in Arkansas, California, Georgia, Iowa, Massachusetts, New Jersey, New York and Texas.

"This study confirms previous evidence, as well as provides new evidence," said principal investigator and UT School of Public Health Associate Professor Kim Waller, Ph.D. "While the absolute risk that an obese woman will have an infant with a birth defect is low, the contribution to public health, given high rates of obesity in the U.S. is significant."

Waller first reported a link between prepregnancy obesity and birth defects in 1994. In this latest study, she collaborated with Shayne Gallaway, a doctoral student, and Mark Canfield, Ph.D., director of the Birth Defects Epidemiology and Surveillance Branch of the Texas Department of State Health Services.

Two of the birth defects studied were already established as having an association with maternal obesity. An association between maternal prepregnancy obesity and five additional birth defects was confirmed during the study, which was supported through a cooperative agreement from the Centers for Disease Control and Prevention (CDC) to the Texas Department of State Health Services Center for Birth Defects Research and Prevention.

"The study provides another reason for women to maintain a healthy weight," said Waller, noting that many pregnancies are unplanned.

Nearly 15,000 mothers - 10,249 of whom had babies with birth defects - were interviewed for the study and identified as thin, overweight or obese based on their body mass index (BMI). Mothers with pre-existing diabetes, or whose children suffered a birth defect based on a single gene disorder or chromosomal abnormalities, were not included. The mothers had babies between 1997 and 2002.

Statistical tests were conducted to identify possible associations between maternal obesity and 16 categories of major birth defects. Seven birth defects were significantly associated with maternal obesity; three were associated with overweight mothers; and one was associated with thin mothers.

Waller, whose nationwide team of collaborators also included researchers from the California Birth Defects Monitoring Program, the National Center on Birth Defects and Developmental Disabilities at CDC, the University of North Carolina School of Public Health and University of Arkansas for Medical Sciences, said a woman can reduce her offspring's risk of birth defects by:

• Taking 400 micrograms of folic acid daily both before pregnancy and during pregnancy - a multivitamin is a convenient way to meet this recommendation;
• And, eating a healthy diet with fortified foods (enriched grain products, including cereals, rice, breads, and pastas) and foods with natural sources of folate (orange juice, green leafy vegetables, beans, peanuts, broccoli, asparagus, peas, and lentils).

Despite the increased risk, pregnant women should not attempt to lose weight unless they are advised to do so by their physician, Waller said. "Some types of dieting may be harmful to the developing baby. Women who are pregnant or may become pregnant should be particularly careful not to use any of the following methods to lose weight: eating very little, eating nothing at all (fasting), over-the-counter laxatives, over-the-counter diuretics, over-the-counter appetite suppressants and herbal preparations; since preliminary evidence suggests these methods can increase birth defect risk."

Maternal obesity was associated with increased risk of spina bifida, heart defects, limb reduction defects, anorectal atresia (malformation of the anus), hypospadias (an abnormal placement of the urethral opening in boys) and two types of hernia - omphalocele and diaphragmatic hernia. Conversely, maternal obesity reduced the risk of gastroschisis, a type of abdominal wall defect.

Despite the associations with maternal obesity, the risk of having a child with a birth defect related to prepregnancy obesity remains low, Waller said.

"To our knowledge, this is the first study to report associations between maternal obesity and anorectal artesia, hypospadias, limb reduction defects, diaphragmatic hernia and omphalocele based on sufficient sample size," Waller wrote in the study.

"As obesity is a common condition and is increasing in prevalence, further studies in this area may help to explain the cause of a substantial portion of certain types of birth defects," Waller said. "Further, obesity prevention efforts are needed to increase the number of women who are of healthy weight before becoming pregnant."

Note: This story has been adapted from a news release issued by The University of Texas

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