In 2009, the Institute of Medicine (IOM) released new guidelines for weight gain during pregnancy. These guidelines recommend how much weight a pregnant woman should gain based on whether she was underweight, healthy weight, overweight, or obese before pregnancy. Researchers funded by the Pregnancy and Perinatology Branch Analyzed data from an NIH study to evaluate pregnancy outcomes within the context of the 2009 IOM guidelines for weight gain during pregnancy.
Most of the women in the study gained more weight during pregnancy than is recommended by the IOM guidelines, and this excessive weight gain had clear medical downsides. With excessive weight gain, women in all weight categories had an increased risk of hypertensive disorders. Furthermore, women who gained excessive weight but who were originally in normal weight and overweight categories also had increased risk of cesarean delivery and of delivering an infant with a birth weight at or above the 90th percentile.
The scientists did not find any consistent relationship between insufficient weight gain and adverse pregnancy outcomes (PMID: 23635732).