Intrapartum Cesarean Delivery in Nulliparas
Intrapartum Cesarean Delivery in Nulliparas
Of the 228 438 deliveries in the entire Consortium on Safe Labor database, 91 424 (40%) were nulliparas. After exclusions, 66 539 met the eligibility criteria (Figure 1). Table 1 describes the demographic data of the eligible cohort grouped by delivery route, where 22% overall had a cesarean delivery. Short stature, African American and Hispanic race/ethnicity, diabetes, hypertension and induced labor were more common in cesarean compared with vaginal deliveries (P<0.001). Greater mean maternal age (26.6±6.4 vs 24.5±5.7 years) and admission BMI (32.6±6.8 vs 29.6±5.4 kg m) were also characteristic of the cesarean delivery group (P<0.001). In addition, those delivered by cesarean had a lower cervical dilation (2.2±1.8 cm) compared with vaginal deliveries (3.3±2.2 cm, P<0.001).
(Enlarge Image)
Figure 1.
Participant selection.
Missing data accounted for 74 (0.1%) maternal age, 3374 (5%) maternal race, 11 811 (17%) admission BMIs and 4257 (6.4%) cervical dilations, with some women having more than one of the variables missing. For the CART analysis, a separate 'missing' branch was created for the age and race variables, leaving 51 104 participants for this analysis. Cervical dilation was the first branch of the CART. Cesarean deliveries occurred in 45%, 25%, 14% and 10% at <1 , 1 to 3, 4 and ≥5 cm, respectively (Figure 2). BMI was the second branch for all dilation categories. A BMI ≥30 kg m was associated with the most cesarean deliveries across all dilation levels. The BMI influence was most evident in the <1cm dilation category with 26% of BMI <25 kg m and 66% of BMI ≥40 kg m having a cesarean delivery. The terminal nodes were varying occurrences of maternal age, gestational age and race, but none of them represented extreme occurrences of cesarean delivery (data not shown). The fewest cesareans (5%) occurred in those ≥5 cm and BMI <25 kg m. Height, diabetes, hypertension and induction did not present as significant contributors over and above the other independent variables included in this model.
(Enlarge Image)
Figure 2.
CART analysis for delivery route in nulliparas. Data presented as CD% and number in each shape (ovals and rectangles), rectangles represent terminal nodes (no other variables had a statistically significant impact on delivery route). Third branches were variations of maternal age, gestational age or race, but none represented extreme occurrences of cesarean delivery (data not shown). CART, classification and regression tree; CD, cesarean delivery; GA, gestational age; VD, vaginal delivery.
Because of the potential correlation between cervical dilation and induction (i.e., more inductions at lower cervical dilations), the induction variable was removed and the analysis was repeated. All branch points and proportions of cesarean deliveries were exactly the same as the analysis with induction (data not shown), which again confirmed that induction was not one of the top hierarchical variables. Maternal age, height and gestational age were also entered into the analysis as continuous variables. The first two branch points (cervical dilation and BMI) and cesarean delivery proportions were exactly the same with varying occurrences of maternal age, height and gestational age in the third branches (data not shown). To assess the impact of missing data, another analysis was performed whereby a 'missing' value was entered as a separate category for cervical dilation and BMI. The results were similar with a first branch point of cervical dilation followed by second branch points of either BMI or induction and then varying occurrences of maternal age, gestational age and BMI as the third branch points (results not shown). The highest proportion of cesarean deliveries still occurred in women with a cervical dilation <1 cm and BMI ≥40 kg m (66%), whereas the fewest occurred in cervical dilation ≥5 cm, <30 years old and not induced (7%). The 'missing' cervical dilation (35% cesarean delivery) branch was further split by induction whereby 47% of induced labors resulted in a cesarean delivery.
In the univariate and multivariate logistic regression analysis, all variables were significantly associated with delivery route except for hypertension in the multivariate analysis (Table 2). Cervical dilation <1 cm (OR 5.1 95% CI: 4.5 to 5.7; reference ≥5 cm) and BMI ≥40 kg m (OR 5.1, 95% CI: 4.6 to 5.7; reference <25.0) had the highest odds for cesarean delivery in the multivariate analysis.
Results
Of the 228 438 deliveries in the entire Consortium on Safe Labor database, 91 424 (40%) were nulliparas. After exclusions, 66 539 met the eligibility criteria (Figure 1). Table 1 describes the demographic data of the eligible cohort grouped by delivery route, where 22% overall had a cesarean delivery. Short stature, African American and Hispanic race/ethnicity, diabetes, hypertension and induced labor were more common in cesarean compared with vaginal deliveries (P<0.001). Greater mean maternal age (26.6±6.4 vs 24.5±5.7 years) and admission BMI (32.6±6.8 vs 29.6±5.4 kg m) were also characteristic of the cesarean delivery group (P<0.001). In addition, those delivered by cesarean had a lower cervical dilation (2.2±1.8 cm) compared with vaginal deliveries (3.3±2.2 cm, P<0.001).
(Enlarge Image)
Figure 1.
Participant selection.
Missing data accounted for 74 (0.1%) maternal age, 3374 (5%) maternal race, 11 811 (17%) admission BMIs and 4257 (6.4%) cervical dilations, with some women having more than one of the variables missing. For the CART analysis, a separate 'missing' branch was created for the age and race variables, leaving 51 104 participants for this analysis. Cervical dilation was the first branch of the CART. Cesarean deliveries occurred in 45%, 25%, 14% and 10% at <1 , 1 to 3, 4 and ≥5 cm, respectively (Figure 2). BMI was the second branch for all dilation categories. A BMI ≥30 kg m was associated with the most cesarean deliveries across all dilation levels. The BMI influence was most evident in the <1cm dilation category with 26% of BMI <25 kg m and 66% of BMI ≥40 kg m having a cesarean delivery. The terminal nodes were varying occurrences of maternal age, gestational age and race, but none of them represented extreme occurrences of cesarean delivery (data not shown). The fewest cesareans (5%) occurred in those ≥5 cm and BMI <25 kg m. Height, diabetes, hypertension and induction did not present as significant contributors over and above the other independent variables included in this model.
(Enlarge Image)
Figure 2.
CART analysis for delivery route in nulliparas. Data presented as CD% and number in each shape (ovals and rectangles), rectangles represent terminal nodes (no other variables had a statistically significant impact on delivery route). Third branches were variations of maternal age, gestational age or race, but none represented extreme occurrences of cesarean delivery (data not shown). CART, classification and regression tree; CD, cesarean delivery; GA, gestational age; VD, vaginal delivery.
Because of the potential correlation between cervical dilation and induction (i.e., more inductions at lower cervical dilations), the induction variable was removed and the analysis was repeated. All branch points and proportions of cesarean deliveries were exactly the same as the analysis with induction (data not shown), which again confirmed that induction was not one of the top hierarchical variables. Maternal age, height and gestational age were also entered into the analysis as continuous variables. The first two branch points (cervical dilation and BMI) and cesarean delivery proportions were exactly the same with varying occurrences of maternal age, height and gestational age in the third branches (data not shown). To assess the impact of missing data, another analysis was performed whereby a 'missing' value was entered as a separate category for cervical dilation and BMI. The results were similar with a first branch point of cervical dilation followed by second branch points of either BMI or induction and then varying occurrences of maternal age, gestational age and BMI as the third branch points (results not shown). The highest proportion of cesarean deliveries still occurred in women with a cervical dilation <1 cm and BMI ≥40 kg m (66%), whereas the fewest occurred in cervical dilation ≥5 cm, <30 years old and not induced (7%). The 'missing' cervical dilation (35% cesarean delivery) branch was further split by induction whereby 47% of induced labors resulted in a cesarean delivery.
In the univariate and multivariate logistic regression analysis, all variables were significantly associated with delivery route except for hypertension in the multivariate analysis (Table 2). Cervical dilation <1 cm (OR 5.1 95% CI: 4.5 to 5.7; reference ≥5 cm) and BMI ≥40 kg m (OR 5.1, 95% CI: 4.6 to 5.7; reference <25.0) had the highest odds for cesarean delivery in the multivariate analysis.
