According to new research from two Pitt professors, eating for two means extra responsibility, not just extra calories.

In a study published in the Wiley Online Library on Nov. 17, Pitt professors Lisa Bodnar and Katherine Himes examined infant mortality rates alongside the mother’s obesity and weight gain during pregnancy from 2003 to 2011 in an observational study focused on Pennsylvania.

With the results, which  Obesity — the journal of the Obesity Society, a nonprofit organization for research, prevention and treatment of obesity — will publish in its February issue, Bodnar and Himes hope to change the way mothers view their own weight and raise awareness about the fight against obesity.

“This finding highlights the importance of discussing weight loss with obese women before pregnancy. Preconception counseling is very important” said Himes, who conducted the  study at the University of Pittsburgh Graduate School of Public Health. 

According to the Magee-Womens Research Institute, infants born to obese mothers are 40 percent more likely to die within their first year than infants born to normal weight mothers.

Bodnar and Himes’ research showed a U-shaped association between weight gain during pregnancy and infant mortality — meaning mothers who gained too little or too much weight were at the greatest risk of losing their infant. Bodnar and Himes do not know yet what caused the greater rate of infant mortality but plan to continue studying the cause in the future.

The study classified mothers into three categories based on their prepregnancy body mass index. The researchers classified women with a BMI less than 18.5 as underweight, a BMI between 18.5 and 24.9 as normal weight — considered optimal for pregnancy — and a BMI greater than 30 as obese.

Himes said one-third of women between 20 and 39, the age when women are most suited to reproduce, are obese.

“One in three women start pregnancy at an unhealthy weight, and more than half of women gain either too much or too little weight during pregnancy,” Bodnar said.

Children of underweight mothers are not at a statistically significant greater risk than children of normal weight mothers, according to Bodnar and Himes’ findings.

In the United States, 6.1 in 1,000 babies born die each year — about 24,000 infants total, according to Bodnar — placing the U.S. birth rate at 26th in the world.

Bodnar, an associate professor in Pitt’s Graduate School of Public Health’s epidemiology department, and her colleagues examined the data from 1.2 million live births from 2003 to 2011 across Pennsylvania. Using birth certificate data, linked birth and infant death records and interviews detailing the mother’s height and weight, Bodnar and her team correlated the weight of the mother with child and infant deaths.

Of the live births examined, 5,530 deaths occurred before the child’s first birthday.

The Institute of Medicine recommends that women of normal weight should gain 25 to 35 pounds, but that obese women should only gain 11 to 20 pounds. Bodnar and Himes, an assistant professor in Pitt’s department of obstetrics and gynecology, measured infant mortality rates for both groups of women. 

Himes said the researchers also studied the joint effect of the variables on mortality rates, while Bodnar said they controlled for other factors that may have influenced infant death rates such as race, gestational age and postpartum factors.

Despite these factors, Bodnar and Himes found that in the underweight and normal weight categories, women who gained more or less than the recommended amount of weight had an increased risk of infant death. Even when obese women gained the recommended weight for their BMI range, their risk of infant death was two times greater than that of women classified in the normal weight category.

Trisha Cousins, a registered dietitian and nutrition and dietetics instructor at Pitt, suggests women ask their physicians about starting exercise programs to reduce the risk of developing gestational diabetes, hypertension and excessive weight gain.

“It is important for pregnant women to make sure they stay hydrated and well nourished,” Cousins said.

Three grants from the National Institutes of Health funded the study. To further the conversation about obesity and women’s health, Bodnar and Himes plan to research why obesity causes higher infant death rates by looking at gestational age.

Bodnar said infant mortality is a huge public health issue, and she hopes her research will motivate change in some U.S. policies related to decreasing obesity, such as how health care providers view obesity.

“We’re hoping to empower family practitioners, primary care doctors, internal medicine doctors and obstetricians to talk about the reproductive consequences of obesity,” Bodnar said. “Women need to make changes before they get pregnant.”