In a land of tiny baby bumps, Nashville star Hayden Panettiere recently came out with a very un-Hollywood admission: She's gained nearly 40 pounds so far during her pregnancy. In an interview with Hello! Magazine, the 5'2" star—who is in her eight month—said: "And the worst part is that my feet are still size five and they're going, 'What's going on with all this weight?'"

Any woman who has to haul around extra pregnancy pudge totally feels her pain (disclosure: I put on 43 and 38 pounds with my two sons, and I'm even shorter than Hayden). So how much pregnancy weight is ideal? And what happens if you go a few donuts over the line?

The target weight gain range for a typical pregnant woman is 25 to 35 pounds, according to guidelines from the Institute of Medicine followed by the American College of Obstetrics and Gynecologists. A large-framed woman should shoot for the top of the range; smaller-framed moms-to-be are best off with about 25. But a woman's starting weight also factors in, explains Bruce Young, MD, Silverman Professor of Obstetrics and Gynecology at NYU Langone Medical Center.

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"If she is overweight or obese we recommend she gain less, and if she is very thin, she should gain more," he says. Reason being that super-slender types, such as marathon runners, have less body fat and nutrients stored up. If an underweight woman doesn't gain well and build up these reserves, Dr. Young adds, "the baby will drain from the mother whatever it needs. It will take glycogen from mom's liver and muscles, and calcium from her bones." Translation: Baby will be fine; you'll be in trouble.

Gaining with gusto isn't as risky as under-eating, but it's not great either. Piling on major pregnancy pounds can cause mom to develop pre-diabetes and have a bigger baby, which ups the child's risk of getting diabetes as an adult, Dr. Young says. And if mom holds on to the extra weight, she'll be more prone to health problems like diabetes and hypertension down the road. Breastfeeding can help women lose the baby weight—women who nurse burn 300 to 500 extra calories per day than those who don't.

Still, the happy news for Hayden, me, and all the many moms who don't quite land in that 25-35-pound zone: It's not a big deal. "Today pregnant women are worried about so many different things," Dr. Young says. "You have to be flexible about weight gain. It's not a problem unless you go well outside the range of normal."

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