Obesity may lead to long-term health problems like high cholesterol, type 2 diabetes, and stroke. But add pregnancy into the equation, and some of these risks are amplified for both mother and child.

Researchers at the Karolinska Institutet in Stockholm, Sweden, analyzed more than 1.5 million Swedish births and found that overweight and obese mothers had a greater risk of preterm deliveries. Preterm births put mothers and their babies in danger, with the potential for more severe health problems for the child down the road. The Karolinska researchers published their findings today in the Journal of the American Medical Association.

Dr. Sven Cnattingius and colleagues investigated the relationship between early pregnancy body mass index (BMI) and preterm delivery using information from the Swedish Medical Birth Register. They divided the preterm deliveries into three groups: extremely preterm (22-27 weeks), very preterm (28-31 weeks), and moderately preterm (32-36 weeks). The risk of "very" and "extremely" preterm deliveries increased with BMI, meaning that overweight and obese women were more likely to have highly preterm deliveries.

“Obesity increases the risk of medically indicated preterm delivery, partly or substantially through obesity-related maternal disorders including preeclampsia,” the researchers wrote.

The maternal obesity problem in Sweden reflects a much greater epidemic, the effects of which are evident in the United States.

“In the United States, where preterm delivery rates are twice as high as in Sweden, the majority of women are either overweight (26 percent) or obese (27.4 percent) in early pregnancy, and severe obesity is much more common than in Sweden," the researchers wrote. "In 2008, extremely preterm births accounted for 0.60 percent of all live single births and 25 percent of all U.S. infant deaths among singletons, and extremely preterm birth is also the leading cause of long-term disability.”

What Can You Do to Protect Yourself?

A number of factors can contribute to obesity, but the same common-sense diet and fitness recommendations apply to all women, regardless of their pregnancy status. Being in contact with a prenatal physician, sticking to a balanced diet, and exercising regularly can make all the difference in the wellness of a mother and her child.

Research also shows that genetic changes leading to obesity can be passed down from an obese mother to her child, but maternal weight loss surgery before pregnancy can help reduce these risks.

According to the Karolinska researchers, obesity has surpassed smoking as the most important preventable risk factor for poor pregnancy outcomes in many countries. Giving up cigarettes during pregnancy is perhaps easier than tackling a weight problem, but all healthy lifestyle changes can have a major impact on infant well-being.

“Considering the high morbidity and mortality among extremely preterm infants, even small absolute differences in risks will have consequences for infant health and survival,” the researchers concluded.

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