Heavier Moms Have Shorter Pregnancies

The risks of being overweight are well-documented, but researchers have found that overweight or obese pregnant women are more likely to give birth prematurely.

Pregnant woman on a scale

Being overweight or obese carries a lot of health risks for everyone, from high blood pressure, insulin resistance, high cholesterol and an increased chance of infection. For pregnant women, there are even more risks, for her and her fetus -- the risk of premature delivery goes up, and those risks increase with the amount of extra weight that the mom-to-be carries.

Premature delivery risk

Delivery before 37 weeks of gestation is considered premature, and the health issues of premature delivery can be relatively mild or quite profound, depending on how far out the delivery was from full-term status (37 to 42 weeks). Birth prior to this point is the leading cause of infant mortality, neonatal illness and long-term disability in children.

Researchers studied the data from 1.59 million Swedish pregnancies via the Swedish Medical Birth Register over a span of nearly twenty years. They checked out the moms’ BMI at their first medical visit and what, if any, pregnancy complications they experienced as well as the length of their pregnancies and information recorded following birth.

They found that the risk of extremely premature (22 to 27 weeks), very premature (28 to 31 weeks) and moderately premature (32 to 36 weeks) deliveries increased with a woman's BMI.

What it means for moms

"The best-case scenario would be attaining an ideal weight prior to pregnancy, but real life doesn’t always work in an ideal way"

Your OB/GYN or midwife will monitor your weight at every visit and counsel you if you seem to be gaining too much or too little, but it has often been thought that if you start out overweight, you shouldn’t try to lose any weight. According to Dr. Raul Artal, a professor and chairman of the department of obstetrics, gynecology and women's health at the Saint Louis University School of Medicine, this is no longer true. "The concept that we propagated for years that pregnancy is not a good time for weight loss and physical activity is wrong," he said.

The best-case scenario would be attaining an ideal weight prior to pregnancy, but real life doesn’t always work in an ideal way. If you do find yourself overweight or obese and pregnant, talk with your doctor about safe and effective exercises and an eating plan that will at least maintain your weight, and ask if weight loss is possible or desirable for you and your baby.

More on pregnancy

Fertility diet: What is a healthy weight for fertility?
8 Expert tips for healthy pregnancy nutrition
Do babies develop favorite foods in the womb?


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