Weight gain during pregnancy in obese women: Should they gain even less?

Background: Nearly 30% of U.S women are obese. Although the Institute of Medicine's (IOM) 2009 gestational weight gain (GWG) guidelines advise obese women to gain 11-20 pounds, it is unclear whether this recommendation is supported by empirical data. We examined GWG and the pregnancy outcomes of small-for-gestational age (SGA), large-for-gestational age (LGA), cesarean delivery, pregnancy-induced hypertension (PIH), and low apgar scores in obese women. Methods: Data from the 2004-6 South Carolina birth certificates were analyzed. 37,288 obese women were categorized by BMI as class I (30.0-34.9), II (35.0-39.9) or III (40.0+) obese. We used the ratio of observed to expected GWG, taking into consideration variation by gestational age (GA) at delivery, to determine adequacy of GWG. Expected GWG was defined using the IOM's 2009 guidelines. Adjusted logistic regression models were used to identify the GWG that corresponded to the lowest odds of poor outcomes. Results: Compared to adequate GWG (78% to 141% of IOM, 11-20 lbs at 40 weeks GA), excessive GWG (>141% of IOM, >20 lbs) significantly increased the odds of cesarean delivery, PIH, and LGA in all classes. Inadequate GWG (>0.071%-78% of IOM, >0-10 lbs) did not increase the odds of any adverse birth outcomes and decreased the odds of cesarean delivery in Class III women. Very inadequate GWG (<=.071% of IOM, <= lbs) increased the odds of SGA in Class II women, but decreased the odds of cesarean delivery in Class II and III. Conclusion: Gaining 1-10 lbs, below the recommendation, was not harmful for obese women.