"It's been well shown that such a patient can lose weight in pregnancy and still be fine," said Dr. Jacques Moritz of St. Luke's-Roosevelt Hospital in New York. "[The guidelines] are still concerned with small babies. That was a problem when women smoked and drank in pregnancy. Now it's just the opposite."
"Women don't need to eat for two but for 1.1," he said.
The authors of the new recommendations noted that good outcomes for both mother and child are achieved "within a range of weight gains." Also, different factors for individual women should be considered, they said.
That means the guidelines should be used "in concert with good clinical judgment as well as a discussion between the woman and her healthcare provider about diet and exercise," they said.
For example, a patient with a BMI of 30 can gain closer to the 20 pounds at the higher end of the range, said Dr. Laura Riley, medical director of labor and delivery at Massachusetts General Hospital in Boston. On the other hand, a pregnant woman with a BMI of 40 "should get closer to the 11 pounds," she said.
Riley said that the major issue behind the new report is that women need to pay closer attention to the guidelines during pregnancy.
"Most women don't listen to the guidelines that were out in 1990," she said. "If they had listened to those guidelines, we would have better outcomes at this point."
The report also calls for further study of pregnancy in obese women, as well as the impacts of gestational weight gain on outcomes for mothers and babies.
Other updates include:
Though there was not as much evidence as there was for singletons, the researchers made provisional guidelines for women giving birth to twins. Normal-weight women should gain 37 to 54 pounds, overweight women should gain 31 to 50 pounds, and obese women should gain 25 to 42 pounds when they're having twins. There was insufficient information for underweight women.
Shorter women don't need to gain toward the lower end of the range for their pre-pregnant BMI. The researchers said there was not sufficient evidence to continue to support this 1990 recommendation.
There is no continued support for women under 20 who become pregnant to gain on the lower end of their range, as younger adolescents often need to gain more to improve their chances of a healthy birth.