Research shows that babies born to obese mothers are at increased risk for dying, particularly in the first weeks of life, compared to babies born to normal-weight mothers.

Given high infant mortality rates in the US as compared to other developed nations, the researchers say, if the results are confirmed, “obesity prevention should be explored as a measure to reduce infant mortality.”

Obese pregnant women are known to be at greater risk of fetal death, while there is also some evidence that death rates are higher among babies born to obese women, according to Dr. Aimin Chen of Creighton University School of Medicine in Omaha, Nebraska and colleagues.

To investigate the relationship in more detail, the researchers compared records for 4,265 babies who died in infancy and 7,293 surviving babies, using data from the 1988 National Maternal and Infant Health Survey.

Among the infants that died, 8.8 percent had obese mothers, compared to 5.9 percent of surviving infants. Babies born to obese women were at greater risk of death in their first year, and were also more likely to die in their first 28 days of life than infants born to normal-weight women.

While risk was increased for obese women no matter how much weight they gained, infant mortality was greatest among women who gained the most weight (0.45 kilogram or one pound and up each week), who were at nearly triple the risk of infant death. Risk was the second-highest for the obese women who gained the least weight (less than 0.15 kg or 0.33 pound a week), who were at 1.75 times greater risk of infant death.

A similar pattern was seen among overweight women, with those who gained the most weight and those who gained the least at highest risk.

A mother’s pre-pregnancy body mass index had the greatest influence on neonatal death. Deaths due to complications of pregnancy, labor and delivery as well as problems related to preterm birth or low birth weight were higher among infants born to all obese women, no matter how much weight a woman gained in pregnancy; however, increased risk of death due to respiratory problems, birth defects, and SIDS was only seen for the obese women in the highest weight-gain category.

One problem with their study, Chen and colleagues point out, is that the data is “old;” since 1988, the prevalence of obesity and the average amount of weight women gain during pregnancy has increased, while infant morality rates have dropped by around 20 percent. However, they note, deaths related to prematurity or low birth weight have not seen declined and may even be on the rise, “which may be related to increasing obesity and infertility treatment.”

SOURCE: Epidemiology, January 2009.