Obesity in Pregnancy May Raise Infant Death Risk

Study Shows Increased Risk of Baby Dying if Mom Is Obese in Early Pregnancy

Reviewed by Laura J. Martin, MD on April 07, 2011

April 7, 2011 -- Babies born to obese moms appear to have an increased risk of dying before birth, at delivery, and during their first year of life, according to a new study.

Maternal obesity during early pregnancy was found to double a baby’s risk for death before delivery and up to one year after birth in a new study from Newcastle University in the U.K.

Nearly half of childbearing-age women in the U.S. are overweight or obese, and maternal obesity is known to increase the risk for gestational diabetes, high blood pressure, surgical delivery, and other complications of pregnancy.

But the impact of a mother’s weight during pregnancy on fetal and infant mortality has not been well understood.

“Obesity is a very common problem in our society and we really need to focus prevention measures on girls and adolescents so that we don’t have so many young women entering pregnancy with this issue,” study researcher Ruth Bell, MD, tells WebMD.

Obesity and Infant Death Risk

Bell and colleagues analyzed data from a survey of close to 41,000 women in the north of England who delivered babies between 2003 and 2005. They compared the mothers’ body mass index (BMI), as calculated from self-reported weight and height, to hospital records of fetal and infant deaths.

After taking into account the impact of other risk factors for death, such as maternal smoking and age and the birth weight of the babies, maternal obesity (BMI of 30 or more) early in pregnancy was associated with a 1.6% risk for having a baby die in the womb or in infancy, compared to a 0.9% risk among women of normal weight.

The researchers concluded that 16 deaths could be expected for every 1,000 babies born to obese women -- eight more than would be expected among normal-weight women during early pregnancy.

One reason for the excess deaths, although not the only one, was the high prevalence of preeclampsia in the obese pregnant women. Preeclampsia is associated with dangerously high blood pressure and protein in the urine.

“There are likely to be a number of reasons why obesity is associated with fetal and infant death and we don’t yet know the full story,” study co-researcher Judith Rankin, MD, says in a news release.

Because the researchers had no information on the women’s diets, exercise patterns, alcohol use, or caffeine consumption, it was not clear if these lifestyle factors influenced the findings.

The study appears in the April issue of the journal Human Reproduction.

Obesity Prevention Efforts

Creighton University School of Medicine assistant professor of medicine Aimin Chen, MD, PhD, says it is increasingly clear that obese women have an increased risk for poorer pregnancy outcomes, even if they don’t develop the complications most commonly associated with obesity.

“Clinicians tend to focus on women with preeclampsia and gestational diabetes, and women without these complications may not get a lot of attention,” Chen tells WebMD. “But even a small increase in BMI over 30 is associated with risk.”

Both researchers agree, however, that pregnancy is no time to diet.

“Prevention efforts should focus on getting women to achieve and maintain a healthy body weight before they get pregnant,” Chen says.

And Bell adds that even though the risk for fetal and infant death is higher for babies born to obese women, the absolute risk is still quite small.

“Most women will have healthy babies regardless of their weight,” she says. “But achieving a healthy weight before pregnancy should be the goal.”

Show Sources


Tennant, P.W.G. Human Reproduction, April 2011.

Ruth Bell, MD, clinical senior lecturer, Institute of Health and Society, Newcastle University, U.K.; associate director, Regional Maternity Survey Office, Newcastle upon Tyne, U.K.

Aimin Chen, assistant professor of medicine, Creighton University School of Medicine, Omaha, Neb.

News release, Human Reproduction.

Vahratian, A. PMC, 2009.

Chen, A. Epidemiology, January 2009.

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