The Association of Maternal Obesity With Fetal pH and Base Deficit at Cesarean Delivery Rodney K. Edwards, MD, MS, Jessica Cantu, MD, Suzanne Cliver, BA, Joseph R. Biggio Jr, MD, John Owen, MD, MSPH, and Alan T. N. Tita, MD, PhD OBJECTIVE: To evaluate the association between mater- nal body mass index (BMI) and umbilical cord acid-base status at the time of cesarean delivery. METHODS: We conducted a retrospective multicenter cohort study using data from the Cesarean Section Registry of the Eunice Kennedy Shriver National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network. Women were included if they delivered a live, nonanomalous singleton at 37–41 weeks of gestation by prelabor cesarean under spinal anesthe- sia. We excluded women with diagnoses that might be associated with uteroplacental insufficiency. Body mass index at delivery was examined both as a continuous and categorical exposure, and acid-base status was based on cord arterial pH and base deficit. RESULTS: There were 5,742 mother–neonate pairs who met criteria for analysis. Among possible confounders (including sociodemographic variables, number of pre- vious uterine incisions, diabetes, hematocrit, neonatal gender, and birth weight), African American race, birth weight, parity, and smoking status were significantly associated with both BMI and acid-base parameters. Adjusted for those four factors, with increasing BMI cate- gory (less than 25, 25–29.9, 30–34.9, 35–39.9, and 40 or higher), mean pH decreased from 7.25 to 7.22 (P,.001), proportion with pH less than 7.1 increased from 3.5% to 7.7% (P5 .011), mean base deficit increased from 4.01 mmol/L to 4.83 mmol/L (P5 .030), and proportion with base deficit of 12 mmol/L or more increased from 0.6% to 4.7% (P5 .003). When BMI was analyzed continuously and adjusted for these confounders, for every 10-unit increase in BMI, cord arterial pH decreased by 0.01 (P,.001) and base deficit increased by 0.26 mmol/L (P5 .005). CONCLUSION: For women undergoing nonemergent prelabor cesarean delivery under spinal anesthesia, fetal pH declines and base deficit rises as maternal BMI increases. (Obstet Gynecol 2013;122:262–7) DOI: 10.1097/AOG.0b013e31829b1e62 LEVEL OF EVIDENCE: II O besity is defined as a body mass index (BMI, calculated as weight (kg)/[height (m)] 2 ) of 30 or higher. 1 The prevalence of obesity in reproductive-aged women in the United States has increased dramatically; currently, 34% of women 20–39 years of age are obese. 2 This problem affects all racial and ethnic groups, but non-Hispanic African American women are at greater risk (47%) than Hispanic women such as Mexican Americans (40%) or non-Hispanic white women (31%). 2 Obesity is associated with an increased risk of many pregnancy complications, and the effect is dose- dependent; these complications include hypertension, gestational diabetes, venous thromboembolism, fetal death, preterm birth, postterm birth, birth defects, mac- rosomia, shoulder dystocia, and anesthesia complica- tions. 3–12 Additionally, obesity is associated with an increased likelihood of labor induction, failure to prog- ress in labor (whether the labor is spontaneous or induced), cesarean delivery, and cesarean delivery com- From the Department of Obstetrics and Gynecology, Division of Maternal-Fetal Medicine, University of Alabama Birmingham School of Medicine, Birmingham, Alabama. The authors thank the Eunice Kennedy Shriver National Institute of Child Health and Human Development, the Maternal-Fetal Medicine Units Network, and the Cesarean Section Registry Protocol Subcommittee for making the data- base available for the project. The contents of this report represent the views of the authors and do not represent the views of the Eunice Kennedy Shriver National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network or the National Institutes of Health. Presented at the 33 rd annual meeting of the Society for Maternal-Fetal Medicine, February 11–16, 2013, San Francisco, California. Corresponding author: Rodney K. Edwards, MD, MS, 176F 10270J, 619 19 th Street South, Birmingham, AL 35249-7333; e-mail: rke@uab.edu. Financial Disclosure The authors did not report any potential conflicts of interest. © 2013 by The American College of Obstetricians and Gynecologists. Published by Lippincott Williams & Wilkins. ISSN: 0029-7844/13 262 VOL. 122, NO. 2, PART 1, AUGUST 2013 OBSTETRICS & GYNECOLOGY