Study questions twin-pregnancy weight-gain limits

NEW YORK (Reuters Health) - In a small new study, women pregnant with twins who gained more weight than current guidelines suggest were not at higher risk of serious pregnancy complications and they gave birth to bigger babies -- a welcome result since twins are more likely than singletons to have low birth weights.

Over a five-year period, 170 patients in a New York City private obstetrics practice gave birth to twins at or near full-term, and mothers who gained more than recommended didn’t have higher rates of gestational diabetes, high blood pressure or pre-eclampsia than women who put on less weight. Plus, the more weight a mother gained, the more likely her babies were to be born weighing above five and a half pounds.

“Not only did we find that it didn’t appear to be bad to gain more weight, it actually appeared to be good,” lead author Dr. Nathan Fox, of Maternal-Fetal Medicine Associates, told Reuters Health.

In 2009, the Institute of Medicine (IOM), a federal advisory organization, recommended ranges for healthy weight-gain during a twin pregnancy. The guidelines, based on a mothers’ pre-pregnancy starting weight, suggested a normal-weight woman put on 37 to 54 pounds, overweight women should gain 31 to 50 pounds and obese women should gain between 25 and 42 pounds.

Fox and colleagues from the Mount Sinai School of Medicine in New York looked at the 170 patients in his practice who delivered twins after 37 weeks gestation or longer (considered full-term) between 2005 and 2010 to see how weight gain affected their pregnancy outcomes.

They found that 40 percent of women who gained less than the IOM’s recommended amount had babies weighing more than 2500 grams (5.5 pounds). That compares to 60.5 percent of women who had normal weight gain by IOM standards and nearly 80 percent of women with what the IOM guidelines would label excessive weight gain.

“There were certain outcomes that were better in the women who gained what they called ‘excessive’ amounts of weight,” Fox said. “For example, our patients who gained more weight had larger babies and lower incidence of low birth weight.”

Twins tend to be born small because their mothers go into labor early, or the babies suffer fetal growth restriction in the crowded womb and don’t grow to their full potential.

“It’s very unusual for twins to be born and to hear someone say the babies are too big,” Fox said. “They are more likely to be in the neonatal unit because they have trouble feeding, breathing and other problems.”

Fox said the study shows how important the relationship is between nutrition and pregnancy, especially in twin pregnancies.

“The public should know there is more and more mounting evidence that in twin pregnancies, nutrition plays a key role in the outcome, much more than we may have originally thought,” he said. “And that focus on nutrition may help improve outcomes with twin pregnancies.”

Although Fox acknowledges more research needs to be done to specifically determine when women pregnant with twins have gained too much weight, he doesn’t limit the amount of weight his patients gain if they are a normal weight when they begin their pregnancies.

Because of the research findings, Fox said he changed the advice he gives his own patients.

“It’s very difficult to know exactly what the right cut off is or how much is too much,” Fox said. “More research needs to be done, but we don’t discourage women from gaining weight. If they are gaining a certain amount, we don’t tell them to slow down. As long as they are eating healthy, we don’t try to have them cut back.”

Dr. Brent Davidson, Service Chief of Women’s Health at Henry Ford Hospital in Detroit, cautioned, “We like not to change recommendations just based on one study.” But, he said, the current findings do make him “less anxious” about his normal weight patients gaining extra weight.

“In normal pregnancy in women with normal weight, if (they) gain more weight, the babies have a lower chance of being small,” Davidson said. “Certainly with twins, small babies are something we worry about. A lot of twins deliver prematurely, so it’s raised a lot of good questions, but I also don’t think we have the final answer.”

Since most study participants were insured and began their pregnancies with normal weight, Davidson said he wonders how the findings would play out among a more diverse group of women who are uninsured, poor or obese.

“We need to look across all populations,” he said. “We still don’t know the impact different socioeconomic groups will have on this data. Many of our patients are starting out severely overweight, and in those patients we need to be a bit more cautious until more studies are done.”

SOURCE: Obstetrics & Gynecology, November 2011.