updated 9/29/2006 3:36:48 AM ET 2006-09-29T07:36:48

Women who gain as little as 7 pounds between pregnancies can put themselves and their babies at medical risk, even if they don’t become overweight, suggests a provocative study of thousands of women.

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Researchers found that gaining weight during that interval — not during the pregnancy itself — raised the risk of such complications as diabetes and high blood pressure during the second pregnancy, and even stillbirth.

Pregnant women with diabetes or high blood pressure are at risk of convulsions or organ damage, which in severe cases, can be fatal.

The results provide new evidence that overweight or obese women who plan to become pregnant should lose weight, and that women with healthy weights should avoid packing on pounds before pregnancy, the researchers said.

The work was reported Thursday in the British medical journal, The Lancet, by Drs. Eduardo Villamor of the Harvard School of Public Health and Sven Cnattingius of the Karolinska Institute in Sweden. They examined records of more than 150,000 Swedish women who delivered two children between 1992 and 2001.

The researchers focused on body-mass index, or BMI, a calculation from a person’s height and weight. They examined the difference between the women’s BMI at the beginning of two consecutive pregnancies. And they examined the likelihood of complications such as high blood pressure, diabetes, the probability of a Caesarean delivery, and stillbirth in the second pregnancy.

Even applies to healthy BMIs
One striking finding was that the risk of complications rose even in women who did not end up overweight, Villamor said Thursday.

For instance, the authors offered the example of a 5-foot-5 woman who weighs 139 pounds before her first pregnancy. That would give her a healthy BMI of 23.

If she gained just 7 pounds before her second pregnancy, she’d move her BMI up a notch to 24, still considered healthy. But the new study suggests she would also raise her risk of becoming diabetic during the second pregnancy by about 30 percent.

Calculate your due dateIf she gained 13 pounds, raising her BMI by 2 units and making her overweight, her diabetes risk would double.

“Those are staggering numbers,” said Dr. Daniel Herron, associate professor of surgery at Mount Sinai Hospital in New York, who was not connected to the study.

“There’s long been a perception that being morbidly obese is associated with diabetes, but we may now be seeing this with relatively small weight increases too,” he said. “That’s news.”

Overall, the new study says gaining 1 or 2 BMI units increases the risk of diabetes and high blood pressure during pregnancy by up to 40 percent. Gaining 3 or more units raised the risk of a stillbirth by 63 percent.

Provocative results
“The results from this study are definitely provocative,” said Dr. Mario Merialdi, a reproductive health specialist at the World Health Organization, who had no ties to the study.

“It is the first study to lend support to a causal relationship between obesity and adverse outcomes,” he said, adding that while previous studies have been suggestive, none has provided the necessary evidence to show a link.

Villamor said he believed the Swedish study would apply to other, more diverse populations, although he said it’s important to confirm that.

Herron agreed: “I think that it does hold a lot of importance for American women as well.”

In an accompanying commentary in The Lancet, Aaron Caughey of the University of California in San Francisco, writes that “as with any groundbreaking study, these findings raise several questions that cannot be answered by the data alone.” One of the study’s limitations is that it could not address the reasons for weight gain, which may in turn be associated with some of the identified health problems.

Breastfeeding practices, Caughey suggests, might explain why some women gained weight between pregnancies and others didn’t. Women who breastfeed typically lose more weight than those who don’t.

Addressing this issue could allow doctors to spot women at risk of becoming obese between pregnancies. Further studies, including those with weight-loss interventions, experts say, are necessary to confirm a definitive link between obesity and pregnancy complications.

But Herron said women should not wait for later research before changing their behavior between pregnancies.

“For anyone who’s ever thought that gaining or losing 7 pounds didn’t make a difference, this should make them think twice,” he said.

© 2012 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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