721: Impact of gestational weight gain by BMI class on cesarean delivery in nulliparous women

Nancy West, Anne Lynch, Jan Hart, Anusha Streubel, Robert McDuffie University of Colorado, Epidemiology, Aurora, CO, University of Colorado, Obstetrics and Gynecology, Aurora, CO, University of Colorado, Pediatrics, Aurora, CO, Kaiser Permanente Colorado, Obstetrics and Gynecology, Denver, CO OBJECTIVE: To construct updated birthweight reference standards using a large, contemporary, and race/ethnically diverse sample in Colorado in order to: 1) provide clinicians with an updated tool for fetal growth assessment and 2) provide updated norms for determination of smalland large for gestational age (SGA and LGA). STUDY DESIGN: In this cross-sectional study, weight-for-gestational age curves for neonates were constructed from birthweight measurements of 57,826 singleton infants (48.6% female). Neonates were born between 20 and 42 weeks gestation during 1999-2010 in the Denver metropolitan area. Gestational age was based on the best obstetrical estimate, which included ultrasound examination in the majority of cases. Sex-specific and combined-sex growth charts were constructed using the 10th, 25th, 50th, 75th, and 90th percentiles. A locally-weighted regression procedure was applied to the empirical weight-forgestational age percentiles. To investigate trends in intrauterine growth, we compared our data to the Lubchenco growth data (Lubchenco, Pediatrics, 1963), which were derived from birthweights of infants born during 1948-1961 in Denver, CO. RESULTS: The updated curves are presented in the figure. On average, male neonates weighed 3284 grams and females weighed 3181 grams. For gestational ages 24-28 weeks, contemporary neonates weighed 182 grams less than the historical neonatal population. Birthweights for gestational ages 29 and 30 weeks were similar between the two populations. For gestational ages 31-42 weeks, contemporary neonates weighed 282 grams more than the historical population. CONCLUSION: We demonstrate changes in birthweights during the past 5 decades in Colorado, including a lower mean weight at early gestational ages and a higher mean weight at later gestational ages. Use of historical growth standards will likely increase misclassification of SGA and LGA in contemporary neonates. These updated norms for intrauterine growth can facilitate monitoring of fetal growth. 721 Impact of gestational weight gain by BMI class on cesarean delivery in nulliparous women Nicole Marshall, Donna Halloran, Judith Chung, Jonathan Snowden, Yvonne Cheng, Kathryn Melsap, Elliot Main, William Gilbert, Aaron Caughey Oregon Health & Science University, Obstetrics and Gynecology, Portland, OR, St. Louis University, Pediatrics, St. Louis, MO, California Maternal Quality Care Collaborative, California Maternal Data Center, Stanford, CA, University of California, San Francisco, Obstetrics and Gynecology, San Francisco, CA OBJECTIVE: The cesarean rate in the United States continues to rise, as does maternal pre-pregnancy weight. While it is clear that obese women have higher rates of cesarean, the impact of gestational weight gain on cesarean rates by body mass index (BMI) group is unclear. The objective of this study was to determine the impact of various amounts of weight gain during pregnancy on cesarean rates by BMI category. STUDY DESIGN: This is a retrospective cohort study of birth records linked to hospital discharge data for all live born singleton infants 37-41 weeks gestation born to nulliparous California residents in 2007. Maternal BMI was determined from self-reported maternal height and prepregnancy weight. The World Health Organization BMI categories were followed including underweight, normal, overweight, and obese. RESULTS: There were 171,382 births meeting study criteria. While increasing maternal BMI was significantly associated with cesarean delivery, rising gestational weight gain increased the rate of cesarean delivery within each BMI group. Normal weight women who gained over 60 lbs and overweight women who gained 40-59 lbs faced a similar rate of cesarean as obese women who gained less than 20 lbs during pregnancy ( 35-40% in all 3 groups). Obese women who gained over 60 lbs had the highest risk of cesarean at 52.5%. CONCLUSION: Gestational weight gain is significantly associated with increased rate of cesarean in nulliparous women of all BMI categories, although the rate remains strongly associated with prepregnancy BMI. By moderating weight gain, women may be able to decrease their rate of cesarean. Figure Figure www.AJOG.org Clinical Ob, Epidemiology, ID, Intrapartum Fetal, Operative Ob, Med-Surg-Diseases, Ob Quality & Safety, Public & Global Health Poster Session V