Weight gain during pregnancy is an important factor in pregnancy outcome. Inadequate weight gain has been associated with increased risk of intrauterine growth retardation (IUGR), preterm birth, low birth weight, and perinatal mortality. Excessive weight gain can also have a negative impact on pregnancy outcome, including elevated risk of a large-for-gestational-age infant, cesarean delivery, and long-term maternal weight retention. In 1990, the Institute of Medicine (IOM) developed a set of recommendations for maternal weight gain based on the pre-pregnancy Body Mass Index (BMI) of the mother. The guidelines advise that those with a BMI of less than 19.8 gain 28 to 40 pounds, those with a BMI of 19.8–26.0 gain 25 to 35 pounds, and those with a BMI of 26.1–29.0 gain 15 to 25 pounds. There are currently no recommendations for women who have a BMI of 29.1 or greater. The IOM convened a workshop in 2006 to assess the impact of pregnancy weight on maternal and child health, and a report from that workshop was released in February 2007.

Data from the National Vital Statistics System show that 13.0 percent of women gained fewer than 16 pounds during pregnancy in 2004; this was most common among non-Hispanic Black women (19.0 percent). Another 20.0 percent of all pregnant women gained more than 40 pounds, which was most common among non-Hispanic White women (22.2 percent). These data suggest that approximately one-third of women had weight gain outside the recommended guidelines; however, this does not account for pre-pregnancy BMI or gestational age. Analyses of other national data sets suggest that approximately two-thirds of women experience weight gain outside of the IOM guidelines.

> Vertical Bar Chart: Weight Gain During Pregnancy, by Race/Ethnicity, 2004