recommendations, gestational weight gain was summarized for women in different prepregnancy body mass index (BMI) groups giving birth to infants weighing between 6.6 and 8.8 lbs., which was considered the normal range of infant birth weight with good outcomes. The range of reported gestational weight gain, which was extremely wide, was then narrowed by the committee to the resultant IOM recommendations (Table 2-2). Abrams and Parker (1990) reported the mean gestational weight gains of women with good outcomes (i.e., infants with birth weights within the normal range) in very similar BMI groups to those used by the IOM committee. The gestational weight gains of women in the underweight and normal-weight groups were generally consistent with the IOM recommendations, but the gains of overweight and obese women exceeded the recommendations. Wells et al. (2006) reported the odds ratio of gaining either above or below the IOM’s recommended range was high in women with a prepregnancy BMI greater than 29 compared with women with prepregnancy BMI of 19.8 to 26—an odds ratio of 19 of gaining above and nearly 7 of gaining below.
The 1990 IOM committee also recommended a rate of weight gain during pregnancy to facilitate the clinical monitoring of weight changes in pregnant women (Institute of Medicine, 1990). The recommendations were based on data from the 1980 National Natality Survey. For normal-weight women, a gain of about 0.9 lb/week in the second and third trimesters was suggested; overweight or obese women were advised to gain slightly less and underweight women slightly more. Studies of rates of gestational weight gain show that women deviate considerably from these recommendations. Data from over 113,000 women in the Pregnancy Risk Assessment Monitoring System (PRAMS) showed that very low rates of gain (<0.26 lb/week) were more prevalent for obese and very obese women, 8 and 19 percent, respectively, than in underweight and normal-weight women, 2 percent in both groups (Dietz et al., 2006). About 10 percent of the women gained weight at twice the recommended weight (more than >1.7 lbs/week).
Studies of the pattern of gestational weight gain help to determine when the greatest rate of gain occurs and how it varies with maternal prepregnancy BMI. Both Butte et al. (2003) and Carmichael et al. (1997) reported greater rates of weight gain in the second trimester compared with the third, with lower average rates in overweight or obese women. However, the pattern of gain differed in a study of 1,367 Filipino women who