The most important message: Get to a healthy weight before you conceive, says the Institute of Medicine in the first national recommendations on pregnancy weight since 1990. It's healthiest for the mother - less chance of pregnancy-related high blood pressure or diabetes, or the need for a C-section - and it's best for the baby, too. Babies born to overweight mothers have a greater risk of premature birth or of later becoming overweight themselves, among other concerns.
Meeting the guidelines could be a tall order, considering that about 55 percent of women of childbearing age are overweight, that preconception care isn't that common and about half of pregnancies are unplanned.
Once a woman's pregnant, the guidelines issued Thursday aren't too different from what obstetricians already recommend, although about half of women don't follow that advice today.
Among the new recommendations:
But pregnancy is not a time to lose weight, stressed guidelines co-author Dr. Anna Maria Siega-Riz of the University of North Carolina, Chapel Hill.
"It's not, 'Hey you gained enough, now you need to stop,"' Siega-Riz said. "Let's take stock of where you're at and start gaining correctly."
Indeed, underweight and normal-weight mothers should put on a pound a week for proper fetal growth in the second and third trimesters, the guidelines say. The overweight and obese need about half a pound a week.
Hopping on the scale during prenatal checkups makes for a sensitive moment, especially in a culture that cherishes the stereotype of late-night ice cream-and-pickles snacks.
Implementing the guidelines may take a move "to change the whole culture about pregnancy" and eating, Siega-Riz said. She noted that in studies of the overweight, "most of these women will tell you that they've never been told how much weight to gain."
The guidelines call for increased nutrition and exercise counseling during pregnancy, saying doctors or midwives may need to consult a dietitian to tailor a woman's care no matter her starting weight. Also, providers should discuss whether a woman plans to breastfeed, which not only is optimal for the baby but helps the new mother shed pounds, too.
"It's really a teachable moment," said guidelines co-author Dr. Patrick Catalano, obstetrics chairman at Ohio's Case Western Reserve University. "When women are pregnant, they may be more accepting" of weight discussions "because it's also in the best interest of their babies."
Obstetricians, who have struggled with how to advise heavier women as U.S. obesity rates have soared over the past two decades, welcomed the guidelines - especially the recognition that babies born too large tend to grow into overweight children at risk for their own health problems. Not too many years ago it was rare to see a 9-pound, or larger, newborn.
"Pregnant women should not be eating for two," said Dr. Ellen J. Landsberger, who specializes in high-risk pregnancies at New York's Montefiore Medical Center. "You want a healthy baby? On both ends, you have to eat the right amount."
But is it realistic for obese women to gain as little as 11 pounds?
"We think it's possible. We also think it will be a challenge," said Cornell University nutrition specialist Dr. Kathleen Rasmussen, who chaired the Institute of Medicine committee.
In the Bronx, Nyree Paten illustrates that challenge: She had been putting on weight for three years and discovered she was pregnant at her peak, just over 300 pounds, seriously obese even for someone 6 feet tall. Her doctor diagnosed diabetes at her first prenatal checkup. Landsberger found Paten, 35, a nutritionist and prescribed insulin for the diabetes. Paten said she's gained only about 2 pounds by week 24, while regular ultrasounds show her baby is growing well.
"Thank God I've been doing good," says Paten, who feels more energetic because she's eating better. So is her 8-year-old son. First to go: sugary sodas and juices in favor of water.
"It's all about knowing and being educated on how to eat," adds Paten, who's lined up the nutritionist to help her lose weight once her baby is born.
The guidelines say women expecting twins can gain more: 37 to 54 pounds for a normal-weight woman, 31 to 50 pounds for the overweight, 25 to 42 pounds for the obese. There's not enough information to set recommendations for triplets or more.
The institute stressed that the guidelines are aimed at U.S. women, not for parts of the world with different nutritional and obstetric needs.