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).