188 Risk factors for nulliparous, term, singleton, vertex cesarean birth

Abstract

To characterize medical, obstetric and demographic risk factors associated with nulliparous, term, singleton, vertex (NTSV) cesarean birth. A population-based study of United States natality records from 2016-2018 evaluated NTSV births. Women with prior deliveries, non-vertex presentation, multiple gestations and gestational age<37 weeks were excluded.The primary outcome was cesarean delivery. Obstetric, demographic and medical factors included maternal age,race, payer, body mass index(BMI), chronic hypertension, gestational hypertension, preeclampsia, pre-gestational and gestational diabetes (DM). We fit multivariable log-linear regression models to determine factors associated with NTSV cesarean. In a sensitivity analysis,we further excluded women with cesarean birth who did not undergo trial of labor. Of 11,622,400 deliveries, 3,671,007 were included. The NTSV cesarean rate was 25.9%. Maternal age 35-39 (RR 1.55, 95%CI 1.54-1.56) and 40-54 (RR 2.11, 95%CI 2.08-2.13) compared to 19-34, pre-pregnancy BMI 30 to<35 kg/m2 (RR 1.65, 95%CI 1.64-1.66), 35 to<40 kg/m2 (RR 1.96, 95%CI 1.94-1.97) and ≥40 kg/m2 (RR 2.04, 95%CI 2.03-2.06) compared to BMI 18.5-24.9 kg/m2, and pre-gestational DM (RR 2.13, 95%CI 2.09-2.16) were associated with increased risk for NTSV cesarean (Table). These associations retained significance in adjusted analyses. The NTSV cesarean rate was 37.2% among the 31.7% of women who had ≥1 of the following:age≥35, BMI≥30 kg/m2 or pre-gestational DM. In contrast, the NTSV cesarean rate was 20.7% among the 68.4% of women without any of these 3 risk factors(p<0.01). Excluding cesarean deliveries without trial of labor (n=585,594), maternal age 35-39(aRR 1.96, 95%CI 1.94-1.98) and 40-54 (aRR 3.12, 95%CI 3.07-3.17) were associated with increased risk of cesarean compared to age 19-34. Higher BMI and older maternal age were associated with 50-100% increased risk of NTSV cesarean. The distribution of these risk factors may be important in interpreting hospital-level cesarean rates and in supporting the validity of the unadjusted NTSV rate as a quality indicator.