(Reuters Health) - Women who gain more weight than recommended while pregnant may increase their chances for serious complications at delivery, a study of more than a half-million births in New York City suggests.

In particular, women who gained more than 20 pounds above the guideline amounts had significantly higher rates of heart failure, severe high blood pressure and needing a transfusion or ventilation, researchers report in Obstetrics & Gynecology.

“We’ve seen a huge surge in . . . maternal mortality in this country, and when we look at the risk factors that are potentially modifiable, gestational weight gain is one that can change throughout pregnancy,” said lead author Dr. Marissa Platner of Emory Healthcare and the Emory School of Medicine in Atlanta, Georgia.

In 2009, the National Academy of Medicine revised guidelines for weight gain during pregnancy based on women’s pre-pregnancy body mass index (BMI, a ratio of weight to height).

Women in the normal BMI range of 18.5-24.9 are encouraged to gain 25 to 35 pounds during pregnancy. Those with a BMI below 18.5 should gain 28 to 40 pounds. Women who are overweight before becoming pregnant should gain less during pregnancy: 15 to 25 pounds for those with a BMI between 25 and 29.9 and just 11 to 20 pounds for those with a BMI of 30 or higher.

Nearly half of all pregnant women in the U.S. gain more than what’s recommended, however, particularly those who are overweight or obese before pregnancy, the authors note.

“It’s really important to optimize your nutrition, diet and exercise before you become pregnant and then during pregnancy,” Platner said in a phone interview. “It’s one of the most important things you can do to affect your pregnancy outcomes.”

For the new study, the researchers analyzed 515,148 singleton births using 2008-2012 New York City data that included information about pre-pregnancy weight and gestational weight gain, as well as serious delivery-related complications such as life-threatening diagnoses, life-saving procedures or death.

About one quarter of the women gained less than recommended, one third gained within the recommended range, another third gained 1-19 pounds more than recommended and 8 percent gained more than 20 pounds above the guideline for their pre-pregnancy BMI.

Overall, the two groups with weight gains above the guideline range had higher rates of complications at delivery. For example, these women were nearly four times more likely to experience heart failure during a procedure, and about two and a half times more likely to require ventilation.

“We saw the increase affect women across the spectrum for all pre-pregnancy weights,” Platner said. “Many physicians and women focus on weight gain only in the overweight or obese groups, but it’s important for everyone to talk about it, not gloss over it because they’re thin before pregnancy.”

Women whose pre-pregnancy BMI was below normal had the highest risks with weight gain above the guideline range. But apart from gestational weight gain, rates of severe complications were highest for women with pre-pregnancy BMI in the obese range.

Women and their doctors need to know about these guidelines for weight gain during pregnancy, said Dr. Michelle Kominiarek, a maternal-fetal medicine specialist with Northwestern Medicine in Chicago, who wasn’t involved in the study.

“A discussion of weight gain goals and methods to achieve those goals should be a priority for providers to have with their patients,” she said by email.

Platner and her team are researching the best ways to talk to women about diet and exercise during pregnancy. For example, that a healthy increase in calorie intake is about 250 per day, she said.

“A healthy diet benefits both the mom and the baby,” said Dr. Sarka Lisonkova of the University of British Columbia in Vancouver, who wasn’t involved in the study.

“Pregnancy is a great motivating factor to start or continue a healthy lifestyle, including a well-balanced diet with plenty of fruits and vegetables,” Lisonkova said by email. “This lifestyle should continue beyond pregnancy.”

SOURCE: bit.ly/2CgCZmo Obstetrics & Gynecology, online March 1, 2019.