Gestational weight gain in obese mothers and associations with fetal growth

Background: In 2009, the Institute of Medicine recommended gestational weight gains (GWGs) of 5-9 kg for all obese women. Recommendations by severity of obesity were not specified because of a lack of available data. Objective: Our objective was to examine associations between GWG and fetal growth in obese women and assess interactions with obesity severity. Design: We used 2004-2006 Pregnancy Nutrition Surveillance System data from 122,327 obese mothers [prepregnant body mass index (BMI; in kg/m(2)) >= 30]. We used logistic regression to estimate measures of fetal growth including small-for-gestational-age, which was defined as birth weight (BW) <2 SDs below the sex and race-ethnicity-specific mean BW (SGA(2SD)), and macrosomia (BW >= 4500 g). We tested for interactions between obesity severity (class I: BMI of 30-34.9; class II: BMI of 35.0-39.9; class III: BMI >= 40) and GWG. Results: Obesity severity modified associations between GWG and fetal growth. Compared with weight gains of 5-9 kg, weight loss in class I women significantly increased the odds of SGA(2SD), whereas a GWG from 0.1 to 4.9 kg was not associated with SGA(2SD) and did not decrease the odds of macrosomia. In class II and III women, compared with weight gains of 5-9 kg, a GWG from -4.9 to +4.9 kg was not associated with SGA(2SD) but did decrease the odds of macrosomia. Conclusions: Our study suggests a GWG below the Institute of Medicine guidelines may be associated with more favorable BW for all obese women, and GWG may need to be further defined by obesity severity. Am J Curt Nutr 2010;92:644-51.