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Combination of Smoking and Excess Weight in Pregnancy Increases Risk of Damage to Infant Heart

Smoking, Obesity, Pregnancy, Birth Defects, Congenital Heart Defects

For women who are pregnant, smoking and excess weight each contribute to the increased risk of birth defects in the developing baby. But add the two together and the risks more than double for congenital heart abnormalities.

Congenital heart defects are abnormalities in the heart’s structure that are present at birth. These happen because of incomplete or abnormal development of the fetus’ heart during the very early weeks of pregnancy. Approximately 8 out of every 1,000 newborns have congenital heart defects, but only 15% of these have known causes.

Dr. Marian Bakker of the department of medical genetics at the University Medical Centre, Groningen and colleagues evaluated nearly 800 fetuses and babies with congenital heart defects, but no other birth defects, between 1997 and 2008. They compared these with 322 born with chromosomal abnormalities, but without heart defects. The babies born to mothers who were both overweight (BMI of 25 or more) and smoked were 2.5 times more likely to have a heart defect than those born to a mom with only one of the two risk factors.

Taken separately, being overweight has been shown to increase the risk of defects in both the ventricular (lower) and atrial (upper) chambers of the heart and in the septum (the wall that divides the two sides of the heart). The risk of pulmonary valve stenosis is also increased. With smoking, typical heart abnormalities include valve defects and heart muscle abnormalities.

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But when considered together, the most common defect of babies born to overweight women who smoked was outflow tract obstructive abnormalities - when blood flow from the ventricles (lower chambers) of the heart to the pulmonary artery or aorta is reduced or blocked. In these babies, the risk more than tripled.

"These results indicate that maternal smoking and overweight may both be involved in the same pathway that causes congenital heart defects," write the authors. The scientists suspect that disturbances in plasma cholesterol may be to blame.

A Kaiser Permanente report earlier this year on ABC News noted that more than 50 percent of women in the United States are overweight or obese at the time they get pregnant. In 2001, the Surgeon General found that only 18 to 25% of all women smokers quit once they became pregnant.

Journal Reference:
Maria E Baardman, Wilhelmina S Kerstjens-Frederikse, et al. Combined adverse effects of maternal smoking and high body mass index on heart development in offspring: evidence for interaction? Heart, 2012; DOI: 10.1136/heartjnl-2011-300822

Photo Credit: Wikimedia Commons