Results
During the study period 33262 births took place at 15 participating hospitals. After exclusion of intrapartum transfers to the delivering hospital (n=506), the final study cohort comprised of 32756 births. Demographic, pre-pregnancy, and pregnancy characteristics of the study population are shown in Table 2. Rates of cesarean without attempting vaginal birth increased with increasing maternal age, increasing BMI, and the presence of pre-pregnancy medical issues and pregnancy complications (Table 2). Rates varied with race and ethnicity: Hispanic women had the lowest rate (17.8%) and African American women had the highest rate (23.0%). One in four women (26.4%) with Class II or III obesity (> 35 kg/m2) had a cesarean with no attempt at vaginal birth. Maternal medical complications such as diabetes and hypertension, and fetal anomalies were also associated with lower rates of attempting vaginal birth. Approximately 1 in 4 multiparous women had a cesarean without attempting vaginal birth compared to approximately 1 in 10 nulliparous women (26.3% vs 10.4%; p<0.001).
The total cesarean rate in the study population was 31.4%: 11.4% were cesareans in women attempting vaginal birth and 20.0% were pre-labor cesareans. Sixty-three percent (6551/10290) of all cesarean births were performed with no attempt at vaginal birth.Approximately 1/3 of cesareans births in nulliparous women, 58.7% of primary cesareans in multiparous women with no history of cesarean, and 39.3% of all primary cesarean births were performed without attempting vaginal birth (Table 3).
Cesarean birth rates in each of the Robson groups are shown in Table 4. Births were non-classifiable due to missing data in 0.5% of the study population. Robson group 5 (previous cesarean, singleton, cephalic ≥37 weeks) made the single greatest contribution to cesarean birth (38.3%). More than nine out of ten (92.5%) cesarean births in Robson group 5 were performed without attempting vaginal birth. In Robson group 10 (singleton, cephalic, pregnancies ≤36 weeks including previous cesareans) 72.9% of cesareans were performed with no attempt at vaginal birth (Table 4). Of the 406 twin pregnancies (in Robson group 8) where Baby A was in a cephalic presentation, 216 (53.2%) had a cesarean without attempting vaginal birth, as did 2418 (68.3%) of the 3542 women with one previous cesarean in Robson group 5.
Of Robson groups 1-4 (singleton term cephalic pregnancies with no history of cesarean), 18.3% (674/3682) of cesareans were performed without an attempt at vaginal birth (Robson groups 2b and 4b).
The NTSV population (Robson groups 1, 2a, and 2b) constituted 37.2% (12201/32756) of all births and contributed 28.8% (2959/10290) of cesareans in the study population. The cesarean rate was 24.3% (2959/12,201) in the NTSV population: 11.1% (1349) after induction of labor, 9.8% (1194) in spontaneous labor, and 3.4% (416) pre-labor cesarean. Approximately 1 in 7 (416/2959) cesareans in the NTSV population were pre-labor.
Pre-labor cesareans in Robson groups 2b and 4b comprised 6.6% (674/10290) of all cesarean births in our study population.
The “indication for cesarean” field was completed for 99.3% of pre-labor cesareans in singleton term cephalic pregnancies with no history of cesarean (Robson groups 2b and 4b). The most common indications were suspected macrosomia (28.9%) and maternal request (18.1%) (Table S1). Placental or cord complications, concern for fetal status, and maternal medical complications each represented approximately 10% of the indications for pre-labor cesarean. Pre-eclampsia/gestational hypertension was the indication in 1.2%, and active genital herpes in 3.1%. Thirteen percent (n=34) of pre-labor cesareans in multiparous women were performed due to complications in previous pregnancies (including shoulder dystocia, third- or fourth-degree tear, and traumatic previous birth).
Birth weight was available for 99.5% (194/195) of the cesareans performed without attempting vaginal birth for suspected macrosomia in Robson groups 2b and 4b. In 77.3% of cases the birth weight was <4500g (150/194). Of the 38 women with gestational diabetes in this group, birth weight was <4500g in 84.2% (n=32).