Global Obesity

A new report from a U-M researcher says that infant mortality rates increase significantly when mothers are obese.

(A/P Kirsty Wigglesworth)

The children of women who are obese are twice as likely to die during the first year of their life than the children of women who are deemed "normal weight," according to researchers from the University of Michigan School of Public Health and the Karolinska Institutet in Stockholm.

Dr. Eduardo Villamor, U-M associate professor of epidemiology and study co-author, said the increased likelihood of infant mortality isn't necessarily due to the frequent complications of pregnancy associated with being overweight such as pre-eclampsia and gestational diabetes.

"The risk increase was more apparent among babies born at term and who died of asphyxia, congenital anomalies or sudden infant death syndrome," Villamor said in a news statement.

The study of 1.85 million live single births in Sweden from 1992 to 2010 analyzed data from the Swedish Medical Birth Register, which, since 1973, has collected information on about 98 percent of all births in that country.

It showed that 81 percent of infants who made it to term died of these conditions or from infection.

The researchers used body-mass index definitions. "Underweight" women have a BMI less than or equal to 18.4, "normal-weight" women have a BMI ranging from 18.5 to 24.9 and "overweight" women have a BMI ranging from 25.0 to 29.9.

"Obese grade I" is a BMI of between 30.0 and 34.9, "obese grade II" is from 35.0 to 39.9, and "obese grade III" is a BMI of greater than 40.0.

Researchers found that 24 percent of women were overweight, and 9 percent were considered obese. They classified the births as very preterm, 22 to 31 weeks, moderately preterm, 32 to 36 weeks, and term births, 37 weeks and up.

Out of this population, there were 5,428 infant deaths, and 11 percent of the deaths were attributed to maternal overweight and obesity, the study said.

For those women with a normal BMI, the number of deaths was 2.4 per 1,000 infants. For women considered severely obese (grade III) the death rate was 5.8 per 1,000.

Infant mortality rates also increased somewhat for overweight and moderately obese mothers.

In previous research, Villamor and the others found that maternal obesity was also associated with obstetric complications and preterm birth.

In this study, they sought to investigate the association with infant deaths, finding that the link between maternal BMI and infant mortality was primarily confined to term births.

There were some increased risks in the neonatal period among women classified as overweight or obese, the study found. Infant mortality risk for very and moderately preterm births was only increased when mom was classified as obese grades II and III.

"Maternal obesity kills babies," Villamor said. "Preventing obesity in women may reduce risk of infant mortality. Weight loss before pregnancy among obese women might reduce the risk of infant death but this is still under investigation."