The association of gestational weight gain with birth weight in obese pregnant women by obesity class and diabetic status: a population-based historical cohort study.

Small-for-gestational-age (SGA) and large-for gestational-age (LGA) infants are associated with increased adverse outcomes. While studies have estimated the association of gestational weight gain with birth weight in obese women, estimates are lacking by obesity class and diabetic status. A population-based historical cohort study of 66,010 obese pregnant women in Missouri delivering liveborn, singleton, term infants in 2002–2008 was conducted. Adjusted odds ratios for SGA and LGA infants were calculated for gestational weight gain categories with multiple logistic regression using the revised Institute of Medicine(IOM) recommended 11–20 pounds as the reference group. A weight gain of 3–10 pounds was not significantly associated with an increased risk of an SGA infant compared to 11–20 pounds in 5/6 obesity class/diabetic status combinations.The exception was Class I Obese non-diabetic women(adjusted odds ratio = 1.28, 95 % confidence interval 1.07, 1.52). When lower amounts of weight gain were considered, diabetic women who gained ≤2 pounds (including women who lost weight) did not have a significantly increased risk of an SGA infant compared to diabetic women who gained 11–20 pounds in any obesity class. Weight gains less than 11–20 pounds were significantly associated with a decreased risk of an LGA infant in 5/6 obesity class/diabetic status combinations. Weight gains lower than the IOM recommendation of 11–20 pounds during pregnancy for obese women generally were significantly associated with decreased risk of LGA infants without being significantly associated with increased risk of SGA infants and differed by obesity class and diabetic status.