Being Big with an Early Baby

Preterm birth risk higher for pregnant women who are overweight or obese

/ Author:  / Reviewed by: Robert Carlson, M.D

(RxWiki News) When a woman becomes pregnant, her health affects her and her baby both. Being overweight or obese can also play a part in how a woman's pregnancy goes.

A recent study found that the risk of having a preemie increased as a woman's weight increased.

The more overweight or obese a pregnant woman was, the more likely it was that she would give birth before she was due.

This was true for extremely early births, before 27 weeks of pregnancy.

"Discuss weight goals with your OB/GYN."

The study, led by Sven Cnattingius, MD, PhD, of the Clinical Epidemiology Unit at Karolinska University Hospital in Sweden, looked at the link between obesity during pregnancy and giving birth early.

The researchers analyzed approximately 1.6 million deliveries of single children to women in Sweden between 1992 and 2010.

Of these, 3,082 were born extremely preterm, between 22 and 27 weeks of pregnancy. Another 6,893 were born very preterm, which is between 28 and 31 weeks of pregnancy.

Additionally, 67,059 were born moderately preterm, which is between 32 and 36 weeks of pregnancy.

The researchers looked at the characteristics of the mothers in these births to determine their risk of delivering a preterm baby based on her body mass index (BMI).

BMI is a ratio of a person's height to weight and is used to determine whether that person is a healthy weight.

In their analysis, the researchers took into account the women's age, number of previous children, smoking history, education, height, country of birth and year she gave birth.

They found that the risk of having a baby early increased as a woman's BMI increased. For women with a normal, healthy weight, just 0.17 percent of births were extremely preterm (between 22 and 27 weeks).

That means 17 babies out of every 10,000 would be born extremely premature to women with a BMI between 18.5 and 25.

For overweight women (BMI between 25 and 30), this rate increased slightly to 22 babies out of every 10,000. For obese women (BMI at 30 or higher), it was 27 babies out of every 10,000, and 35 babies out of 10,000 for those with a BMI between 35 and 40.

Women who were extremely obese, with a BMI over 40, had a rate of 52 babies per 10,000 being born between 22 and 27 weeks.

The rates of very preterm and moderately preterm births also increased as women's BMI increased.

Therefore, for the Swedish population studied, "Maternal overweight and obesity during pregnancy were associated with increased risks of preterm delivery, especially extremely preterm delivery," the researchers concluded.

The study was published June 11 in JAMA. The research was funded by grants from the Karolinska Institutet.

Other than one author's grant from the Swedish Research Council for Working Life and Social Health, the authors reported no disclosures or conflicts of interest.

Reviewed by: 
Review Date: 
June 8, 2013
Last Updated:
August 7, 2013