Topics: Obstetric Complications, Neonatal Morbidity/MortalityS tudies investigating the maternal and neonatal risks of elective cesarean deliveries at 37 to 41 weeks' gestation have found a higher risk of neonatal morbidity for deliveries before 39 weeks' gestation compared with those at 39 weeks' gestation. However, to evaluate overall risk, risk of a cesarean delivery (CD) at a given gestational age needs to be compared to the risks in women who continue their pregnancy after that point. This secondary analysis was undertaken to compare the risks of elective repeat CD at each gestational age beginning at 37 weeks with the maternal and neonatal risks of pregnancy continuation beyond that time point.Data from the Cesarean Section Registry of the Eunice Kennedy Shriver National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network included information on consecutive repeat CDs performed at 19 US academic centers from 1999 to 2002. The composite maternal outcome included death, pulmonary edema, cesarean hysterectomy, pelvic or abdominal abscess, deep vein thrombosis or pulmonary embolism, pneumonia, or blood transfusion. Composite neonatal outcome included death, respiratory distress, transient tachypnea, necrotizing enterocolitis, sepsis, mechanical ventilation, seizure, hypoxic-ischemic encephalopathy, NICU admission or 5-minute Apgar score of r3. Outcomes after elective, repeat CD without labor at each week of gestational age were compared with those for all women who were delivered later as a result of labor onset, obstetric indications, or both. Potential confounders that were controlled for were race and ethnicity, number of prior CDs, marital status, payer, smoking, medical history, maternal age, and body mass index.Of 378,063 women enrolled in the registry, 23,794 had repeat CD at Z37 weeks' gestation; 14,993 of these underwent CD before labor and with no medical or obstetric indications. Among the women in the study population, 12.1%, 30.6%, 41.7%, 11.0%, 3.8%, and 0.9% were delivered at 37, 38, 39, 40, 41, and Z42 weeks' completed gestation, respectively. Compared with women delivered at a later time, those delivered at earlier, specific gestational ages were more often affected by medical disorders, had >1 prior CD, and were more likely white, married, and insured. The incidence of blood transfusion was higher with elective deliveries at 37 weeks compared with women expectantly managed (1.9% vs. 1.1%; P = 0.016). Pneumonia was more common in those women who delivered at 37 weeks' gestation compared to those who delivered later (0.3% vs. 0.09%; P = 0.042). Cesarean hysterectomy was more frequent in women who were still pregnant after 39 weeks (0.2% vs. 0.4%; P = 0.035). Elective CD at 37 weeks carried significantly higher risks of adverse maternal outcomes [odds ratio (OR), 1.56; 95% confidence interval (CI), 1.06-2.31]; elective delivery at 39 weeks led to better maternal outcomes compared with continuation of pregnancy (odds ratio, 0.51; 95% CI, 0.36-0.72). The ORs for el...