Differences in Institutional Cesarean Delivery Rates: The Role of Pain Management

Analysis

We compared demographic characteristics and rates of selected outcomes between hospitals, using the chi-square statistic for categoric variables and the Student t test statistic for continuous variables. When expected cell frequencies were less than 2, we used the Fisher exact test for categoric variables instead of the chi-square statistic. The type I error, 2-sided a, was set at 0.05. Multivariate analysis was undertaken using unconditional logistic regression. We obtained maximum likelihood estimates of the odds ratios using the logistic model. We calculated 95% confidence intervals using the estimates of the standard error derived from the model.

Results

Phase I

Comparing cesarean delivery rates from our retrospective study of 857 births, the crude nulliparous rate at BC Women’s was 20.7%, while at Burnaby it was 6.7% (P <.0001). We examined a number of demographic and obstetric factors to determine if they would explain the reason for the increased rate at BC Women’s.

Women at Burnaby were younger, more likely to be single, and white (P <.0001, Table 1). A larger proportion of women at BC Women’s were Asian. Cesarean delivery rates did not differ between white and Asian women (9.1% vs 9.3%) at Burnaby, but there was a marked difference (18% vs 28.6%) at BC Women’s (data not shown). Women arrived earlier in labor at BC Women’s Table 2. The lengths of the first and second stages were longer at BC Women’s, as was the length of time membranes were ruptured. Time from admission to delivery was also significantly increased at BC Women’s.

Rates of obstetric interventions were compared between the 2 settings Table 2. Rate of induction of labor was not different between the 2 hospitals; however, augmentation of labor with oxytocin occurred significantly more frequently at Burnaby than at BC Women’s. Artificial rupture of membranes during labor was performed significantly more often at BC Women’s than at Burnaby. BC Women’s primarily used epidural analgesia, while Burnaby used intramuscular or intravenous administration of meperidine (Demerol). Use of Entonox (nitrous oxygen and oxygen) was also significantly different. Electronic fetal monitoring (EFM) was used for almost all patients at both hospitals; however, at Burnaby nurses were more likely to obtain only a baseline or admission fetal monitoring record, or to monitor intermittently. BC Women’s, on the other hand, was more likely to employ EFM continuously. Increased use of EFM both with and without epidural analgesia resulted in women being confined to bed more often, since remote methods (telemetry) of monitoring fetal heart rates were rarely used.

Overall rates of assisted vaginal deliveries at the 2 hospitals were not different, although forceps were used more frequently at BC Women’s and vacuum extraction at Burnaby. More frequent use of cesarean delivery at BC Women’s was not associated with an improvement in selected maternal/newborn outcomes (postpartum hemorrhage and 5-minute APGAR score <7). Postpartum infections were significantly more common at BC Women’s (P <.0001).

Data were analyzed for each hospital separately to determine all the factors contributing to cesarean delivery in each Table 3. After regressing all the demographic factors in a multiple regression model with cesarean delivery as the dependant variable for each hospital, only age remained significant. To evaluate the role of obstetric interventions for each hospital each intervention was entered separately, the most significant retained, and the process repeated with the next most significant retained until no other variables remained significantly associated with cesarean delivery. Age was retained in all the models.

In Burnaby, patient age, cervical dilatation on admission to the hospital, induction, epidural analgesia, and augmentation with oxytocin were important. At BC Women’s the same factors were important, as well as race/ethnicity (white vs nonwhite). Use of electronic fetal monitoring, Entonox, and intravenous or intramuscular narcotics did not predict cesarean delivery in either setting.

To compare the 2 hospitals in cesarean delivery rate we created a model combining data from both institutions. With both in the model, we could quantify the risk for cesarean delivery in one hospital compared with the other. First we examined the role of demographic factors in accounting for differences in cesarean delivery rate. Adjusting for age, the odds ratio (OR) for cesarean delivery at BC Women’s compared with Burnaby was 3.4 (95% confidence interval [CI], 2.1-5.4).

Cervical dilatation on admission, oxytocin augmentation, and epidural analgesia remained statistically significant in addition to age for predicting cesarean delivery. When age, augmentation, and cervical dilatation were retained in the model there remained a statistically significant difference between the 2 hospitals; the OR for BC Women’s versus Burnaby for cesarean delivery was 3.8 (95% CI, 2.3- 6.3). When we adjusted for epidural in addition, the OR for BC Women’s versus Burnaby dropped to 2.0 (95% CI, 1.09-3.5); the difference became only marginally statistically significant. The principal factor associated with the difference in cesarean delivery rate between the 2 hospitals, therefore, was use of epidural analgesia.