"The take-home message is that you can eat well during your pregnancy without overeating, and pregnancy should not be a license to overeat, and pregnancy should not be a contributing factor to the epidemic of obesity in this country," researcher Yvonne S. Thornton, MD, MPH, tells WebMD.
Thornton's findings, published in the June edition of the Journal of the National Medical Association, go further than the Institute of Medicine (IOM) did in its new guidelines for pregnancy weight.
The IOM recommends that obese women gain 11-20 pounds during pregnancy. Thornton's team argues that obese women may have healthy pregnancies maintaining their weight, provided they have professional nutritional guidance -- and accountability about what they eat.
Pregnancy "is not a time to eat twice as much, but twice as well," Thornton says.
Pregnancy Weight Study
Thornton's study included 232 New York state women who were obese when they got pregnant. The women's BMI (body mass index) ranged from 30 to 69, averaging in the upper 30s.
All of the women got information about nutrition during pregnancy. Half of the women also got a personalized healthy eating program and kept food diaries, which were reviewed at each prenatal checkup. For comparison, the other half of the group didn't get eating plans and didn't keep food diaries.
Thornton says she deliberately didn't use the word "diet" because she considers it "an emotionally charged word" and because the study wasn't about losing weight during pregnancy.
"We're not saying that pregnant women should lose weight. We're not advocating that," Thornton says. "We're saying, 'Forget about the pounds, already ... Let's talk about eating well and whatever happens, happens.'"
Thornton likens the food diary reviews to monitoring drivers' speed.
"If it says 55 miles an hour, you know most of us don't go 55 miles an hour. But if there's a police officer there, we're going 55 miles an hour. And that's the same thing with my study."
For instance, Thornton says a patient told her that she was craving chocolate cake but decided to get fruit instead because she knew she would have to write it down.
Obesity and Pregnancy: Study's Results
Overall, women who gained less than 15 pounds during the pregnancy were more likely to be in the group that kept the food diaries than in the comparison group, and they were less likely to develop gestational diabetes, preeclampsia, undergo cesarean section, or have labor induced.
The women who got personalized nutritional advice and who were asked to keep food diaries gained an average of 11 pounds during their pregnancies. Women in the comparison group gained an average of 31 pounds.
Most of the pregnant women who got personalized nutritional advice and who kept food diaries -- 90 out of 116 women -- followed the study's ground rules. They gained even less weight -- an average of 5 pounds during their pregnancies.
In contrast, women who didn't stick to their personalized eating programs and didn't turn in their food diaries gained more weight -- 31 pounds, on average, which is as much as women in the comparison group.
No side effects were reported during the study, and the babies were born healthy and at a normal weight. "They were not little peanuts," Thornton says.
Obesity and Pregnancy: Don't Obsess
Thornton's study was "very interesting and timely work ... an admirable research effort," Bill Barth Jr., MD, tells WebMD. Barth is an associate professor at Harvard Medical School and chief of the division of maternal-fetal medicine at Massachusetts General Hospital.
"The study, if it's confirmed by larger studies, suggests that women who have a body mass index over 30 may not need to gain weight at all if in a supervised program," Barth says. "Ideally, this would be covered by a clinical nutritionist or a nurse or a physician with special training and experience in dietary counseling."
Michelle Owens, MD, assistant professor of maternal-fetal medicine at the University of Mississippi Medical Center in Jackson, Miss., has had many obese patients who've gotten pregnant.
Praising Thornton's study, Owens says people tend to "obsess" about how much weight they should gain during pregnancy.
"But in actuality, those numbers are firmly rooted in basic behavioral and nutritional habits," Owens says. "I think that that needs to be cornerstone, rather than obsessing over the number, because you can still make a significant impact without necessarily meeting a numeric goal."
Pregnancy can be an ideal time to move toward healthier eating, Owens notes.
"I think a lot of times with pregnant ladies, you can motivate someone to do things for themselves during pregnancy that you ordinarily might not be able to motivate them to do, because it's not just about them but it's also about the outcomes for their babies, as well."