Women who are extremely obese may not need to gain that much weight during pregnancy, and those who don't add too many pounds may find themselves and their babies healthier.
The data was presented at the Society for Maternal-Fetal Medicine's annual meeting. The study looked at data on 73,977 women who gave birth to one child between 2004 and 2008.
Among the women, 4 percent were underweight, 48 percent were normal weight, 24 percent were overweight, and 24 percent were obese. In the obese category, 13 percent were class one (having a BMI of 30 to 34.99), 6 percent were class two (a BMI of 35 to 39.99) and 5 percent were class 3 (a BMI of 40 or above).
Gaining less weight than recommended during the second and third trimester for women who fell under class two or three obesity was not linked with having a baby considered small for its gestational age or with poor outcomes for mothers. However, gaining less weight than advised during the second and third trimester for women in other weight categories was associated with having a smaller baby.
In all BMI categories, gaining more weight than advised during the second and third trimesters was linked with a greater risk of giving birth to a baby large for its gestational age.
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In 2009, the Institute of Medicine issued revised guidelines for weight gain during pregnancy.
For women who are overweight (a BMI of 25 to 29.9), a total weight gain range of 15 to 25 pounds was recommended. For obese women (a BMI of 30 or more) the recommendation was a total gain range of 11 to 20 pounds.
"The study suggests that even the recommended amounts of weight gain might be more than is needed for the most obese women," said Dr. Eva Pressman, director of Maternal Fetal Medicine at New York's University of Rochester Medical Center, in a news release.
