Even women who succeed in controlling their weight before pregnancy tend to gain too much weight while they're carrying a child, say Anna Maria Siega-Riz, PhD, RD, and colleagues at the University of North Carolina at Chapel Hill.
"When they are not pregnant, many women are really trying to hold their weight down. But when they become pregnant the message they get is 'Eat for two; give in to your cravings,'" Siega-Riz tells WebMD.
The UNC researchers asked 1,223 women who had just become pregnant about their previous dietary habits. About half the women had restrained their eating habits in some way. They simply cut back on what they ate, followed specific diet plans, and/or cycled between gaining and losing weight.
Regardless of how they did it, all normal-weight, overweight, or obese women who had tried to restrict their diets gained more weight during pregnancy than did women who did not diet before pregnancy.
Moreover, the pre-pregnancy dieters gained more weight during pregnancy than doctors recommend -- putting themselves and their babies at risk.
Women who gain too much weight during pregnancy have more C-sections, more preeclampsia, and are more likely to have babies with growth problems, says obstetrician J. Christopher Glantz, MD, MPH, director of the perinatal outreach program at the University of Rochester Medical Center.
"You might think people who are dieting before pregnancy would tend to gain less weight. Not only is that not true, this study shows that in pretty much all weight categories, the restrained eaters seem to gain more weight once they get pregnant," Glantz tells WebMD.
Surprisingly, normal-weight women don't need much more food once they're pregnant:
It's a different story only for women who are underweight before pregnancy, but who restrict their diets anyway. These women, Siega-Riz and colleagues found, did not gain enough weight during pregnancy -- and many likely suffer from eating disorders.