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Obstetrics & Gynecology 2003;102:1358-1365
© 2003 by The American College of Obstetricians and Gynecologists
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ORIGINAL RESEARCH

Impact of Sociodemographic and Hospital Factors on Attempts at Vaginal Birth After Cesarean Delivery

Rebecca Dunsmoor-Su, MD, MSCE, Mary Sammel, PhD, Erika Stevens, MS, Jeffrey L. Peipert, MD and George Macones, MD, MSCE

From the Department of Obstetrics and Gynecology, University of Pennsylvania Health System; Center for Clinical Epidemiology and Biostatistics and Department of Biostatistics and Epidemiology, University of Pennsylvania School of Medicine; Leonard Davis Institute for Health Economics, University of Pennsylvania, Philadelphia, Pennsylvania; and Women and Infants Hospital, Brown University School of Medicine, Providence, Rhode Island.

Address reprint requests to: George Macones, MD, MSCE, Director, Maternal Fetal Medicine, 2000 Courtyard Building, 3400 Spruce Street, Philadelphia, PA 19104-4283; E-mail: gmacones{at}mail.obgyn.upenn.edu.


   ABSTRACT
TOP
ABSTRACT
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
OBJECTIVE: To estimate the clinical and nonclinical factors associated with whether a patient attempts a trial of labor after previous cesarean delivery or elects to have a repeat cesarean delivery.

METHODS: We conducted a retrospective, cohort study comparing all women with previous low transverse cesarean delivery who attempted a trial of labor with those who elected to have a repeat cesarean delivery. Data from 17 hospital sites for the period 1995–1998 were included, for a total of 15,172 patients. Bivariate, site-adjusted, and multivariable logistic regression analyses were used.

RESULTS: Odds of trial of labor by hospital were not uniform in the unadjusted or adjusted analyses. The odds of trial of labor decreased significantly with increasing age, gravidity, and number of previous cesarean deliveries. Medicaid patients had higher odds of trial of labor than did privately insured patients (odds ratio [OR] 1.37 [95% confidence interval (CI) 1.20, 1.55]). Patients with nonrecurrent indication for previous cesarean delivery had generally higher odds of trial of labor than did those with a recurrent indication. Black women were more likely to attempt trial of labor than were white women (OR 2.17 [95% CI 1.83, 2.56] for those with a nonrecurrent indication).

CONCLUSION: Clinical and nonclinical factors influence rates of attempted vaginal birth after cesarean delivery.

There are approximately 4 million births in the United States per year, of which approximately 20% are by cesarean delivery. There are many legitimate indications for performing a cesarean delivery, including fetal mal-presentation, nonreassuring fetal heart rate tracing during labor, and cephalopelvic disproportion. However, one of the most common indications for cesarean delivery is a prior cesarean delivery (ie, elective, repeat cesarean delivery).1–7

Over the past 2 decades, obstetricians have been encouraged to offer women with a previous low transverse segment cesarean delivery an attempt at vaginal birth. Although early research suggested reasonable success rates in attempts at vaginal birth after cesarean delivery (VBAC), recent work has emphasized the maternal and neonatal risks associated with VBAC.8–25

Several studies have assessed risk factors for cesarean delivery for first births and have found that rates vary according to hospital factors, patient populations, and even individual physician practice characteristics.26–30 Similar work has been done with the use of vital statistics data to compare women who have repeat cesarean deliveries with those who have a successful VBAC.30–35 There is little research, however, that evaluates the factors associated with the decision of whether a patient undergoes a VBAC attempt or an elective repeat cesarean delivery. We believe that understanding current patterns of VBAC attempts might help to ensure that the same standards are applied to all subsets of pregnant women. Thus, the purpose of this study was to estimate the clinical and nonclinical factors associated with whether a patient attempts a trial of labor after previous cesarean delivery or elects to have a repeat cesarean delivery.


   MATERIALS AND METHODS
TOP
ABSTRACT
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
We conducted a retrospective, cohort study at 17 participating hospitals in the northeastern United States. Eleven of the hospitals are teaching facilities, defined as having an obstetrics and gynecology residency program, and six of these are tertiary care centers (defined as university referral centers with obstetrics and gynecology residency programs). The remaining six hospitals are referred to as community hospitals, defined as non-teaching, nontertiary care sites. The neonatal intensive care level for each hospital is noted in Table 1Go. Patients were identified by a medical record search for those with a discharge diagnosis of "previous cesarean section: delivered" (which in pilot studies captured 100% of this patient population) at all participating hospitals between 1995 and 1998.


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  		Table 1. Unadjusted Trial of Labor Rate by Hospital Site
 
The delivery admission record was abstracted with a structured abstract to collect demographic, obstetric, medical, and social factors, as well as pregnancy outcome. We were unable to collect specific information regarding the outcome of prior cesarean deliveries from the prior pregnancies. Thus, for example, the type of prior cesarean delivery scar was ascertained from the index pregnancy record. Abstractors were trained with standardized procedures at the start of the study.

From the initial cohort, we excluded women who had a prior classic cesarean delivery or prior T-shaped incision. Patients for whom this was not the first trial of labor after cesarean delivery were also excluded, because this might correlate strongly with attempting VBAC a second time (see Figure 1Go). Thus, we included subjects with one prior cesarean delivery or more who were faced with the decision of whether to undergo an initial VBAC attempt or an elective repeat cesarean delivery. We believe that from a clinical perspective, this is the critical group to study.



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  		Figure 1. Study subject selection.

Dunsmoor-Su. Clinical and Nonclinical Factors and VBAC Attempts. Obstet Gynecol 2003.

 
The primary comparison was of factors associated with whether a patient elected a VBAC attempt or a repeat cesarean delivery. Bivariate analyses were undertaken with Student t test for continuous factors, Wilcoxon rank-sum test for nonparametric and ordinal variables, and {chi}2 tests of association for categoric factors (Stata SE 7.0, College Park, TX). We focused on obstetric factors, hospital factors (level of nursery, presence of an obstetric residency program), and maternal medical or social historical factors. Risk factors were then stratified by hospital to assess possible confounding and effect modification, with Mantel-Haenszel tests for categoric factors and logistic regression with separate indicator functions for each hospital for continuous factors. Linearity of the association between age and trial of labor was assessed graphically with smoothed scatter plots36 and by testing the addition of an age2 term in the logistic regression model. Dummy variables were used to represent hospitals in the logistic regression model. This approach allowed for estimation of different associations by hospital while providing control of potential confounding by site.

There were several predetermined, clinically relevant interactions of interest that were evaluated, specifically the relationship between race, indication for prior cesarean delivery, and VBAC attempt; no other possible effect modification was addressed so as to minimize chance findings. Multivariable logistic regression models were constructed with all significant (Wald test P < .05) risk factors, as well as confounding factors identified from stratified analyses.36 All main effects and interaction terms were tested for significance with likelihood ratio tests. Forward and backward selection techniques were used, with the criterion for inclusion being likelihood ratio test with a P value < .05. Both techniques yielded the same final model. Two-tailed interpretations were used for all P values. We present relevant associations with odds ratios and 95% confidence intervals. This research received institutional review board approval from each participating institution.


   RESULTS
TOP
ABSTRACT
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
The total number of patients included in the analysis was 15,172. The overall trial of labor rate (unadjusted) was 50.05% of all eligible patients. The proportion of women attempting a VBAC varied significantly by hospital in both unadjusted and adjusted analyses, from a low of 38% to a high of 65% (Table 1Go and Figure 2Go). The odds by hospital site vary independently of teaching status, tertiary care status, or level of neonatal intensive care unit (data not presented).



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  		Figure 2. Odds ratios (adjusted for age, gravidity, number of previous cesarean deliveries, race, indication for previous cesarean delivery, and payor) and 95% confidence intervals for trial of labor, by hospital site.

Dunsmoor-Su. Clinical and Nonclinical Factors and VBAC Attempts. Obstet Gynecol 2003.

 
The unadjusted comparison of factors between those who underwent a VBAC attempt and those who opted for a repeat cesarean delivery are presented in Table 2Go. As expected, increasing number of prior cesarean deliveries was associated with an increased likelihood of repeat cesarean delivery, as was the presence of maternal medical problems and a nonrecurrent indication for prior cesarean. This unadjusted analysis also suggested an association between ethnicity and insurer and whether a subject attempts VBAC.


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  		Table 2. Demographic Characteristics of Eligible Patients
 
Hospital-adjusted associations are presented in Table 3Go, in which an odds ratio greater than 1 indicates increased rates of VBAC attempt over the reference group. In this analysis, increased VBAC attempt was associated with black and Asian race, Medicaid or other insurance, and a nonrecurrent indication for the prior cesarean delivery. An increase in the number of prior cesarean deliveries, a positive medical history (hypertension, diabetes, connective tissue disease), and prior abdominal surgery (appendectomy, cholecystectomy, ovarian or tubal surgery) were associated with a decreased likelihood of VBAC attempt. Adjusted analysis largely confirmed the observations in the site-adjusted analysis (Table 4Go). In this analysis, after controlling for confounding factors (including hospital site), Medicaid insurance was associated with an increased likelihood of VBAC attempt, whereas the number of prior cesarean deliveries was associated with a decreased likelihood of VBAC attempt. The association between race and VBAC attempt varied somewhat by the indication for prior cesarean delivery. Across all of the indication categories, black and Asian women had a higher VBAC attempt rate than did white women. Across all indications, Hispanic women had rates of trial of labor to similar those for white women. We also performed an analysis while limiting our data set to women with only a single prior cesarean delivery. In this analysis, the same associations that were seen in the overall analysis persisted (Table 4Go).


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  		Table 3. Bivariate Associations of Trial of Labor With Demographic Factor, Adjusted for Hospital Site
 

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  		Table 4. Multivariable Model of Trial of Labor by Demographic Factor, Adjusted for Hospital*
 

   DISCUSSION
TOP
ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
Early research on VBAC was centered on the favorable rates of successful VBAC. Most recently, attention has been focused on safety issues—specifically the small risk of uterine rupture, with its effect on both maternal and neonatal outcome. Because of both the potential risks and benefits of VBAC attempts, it is important to understand the factors that are associated with whether or not a trial of labor is undertaken. Prior work has compared clinical and nonclinical factors between women who have a repeat cesarean delivery (either elective or after a failed VBAC) with those who have successful VBAC.31–35 Although this work is important, the more clinically relevant comparison is between those who attempt VBAC (whether they fail or not) and those who opt for elective repeat cesarean delivery. Unique to this work, we are able to directly examine the difference between the population of women who attempt VBAC and those who opt for an elective repeat cesarean. If there is no increased risk associated with VBAC for a particular population, yet they have a significantly lower rate of trial of labor, it is important to note this so that interventions and education can be targeted to these women, their physicians, and their hospitals.

Our study demonstrates that, after controlling for covariates such as age, gravidity, number of previous cesarean deliveries, race, and payor, several clinical and nonclinical factors influence VBAC attempt rates. Interestingly, hospital site proved to be one of the most important factors in determining the VBAC attempt rate. The differences seen among the hospitals were not associated with any of the hospital-specific factors, namely tertiary care status, teaching hospital status, or level of neonatal intensive care unit. Likewise, patient mix also did not account for the differences in VBAC attempts seen between hospitals. Quite simply, there is large variation in practice from site to site that cannot be accounted for by differences in the clinical populations or type of hospital.

Several patient factors were associated with differences in trial of labor rates. Increasing gravidity is associated with lower odds of trial of labor after adjusting for age and number of previous cesarean deliveries. Additionally, as expected, increased number of previous cesarean deliveries independently reduces the likelihood of a VBAC attempt. This follows clinical recommendations at the time of this analysis, which encouraged VBAC most strongly in women with one previous cesarean delivery.37 When indication for previous cesarean delivery is assessed independently of race (comparing rates within race categories), the pattern is toward higher rates of trial of labor among women with nonrecurrent indication for prior cesarean (such as malpresentation).

Interestingly, markers of socioeconomic status have the most profound effect on VBAC attempt rates. Most notably, among the payor categories, Medicaid patients had a 37% increase in VBAC attempt rates over privately insured or managed care patients. The difference in VBAC attempt rates persisted after controlling for patient mix and other covariates. Ethnicity also was associated with VBAC attempts. Black women had a higher trial of labor rate than did white women, regardless of indication for previous cesarean delivery, and they had the highest rate among women with recurrent indication for previous cesarean delivery. We cannot precisely determine why subjects with Medicaid insurance and of black or Asian ethnicity have higher VBAC attempt rates. In theory, the differences observed could occur for one of several reasons, including differential providing of information to subpopulations; increased acceptance of recommendations by health care providers by subpopulations; cultural differences in the importance of vaginal delivery; and differences in level of provider experience with subpopulations.

In the interpretation of our study, the following limitations must be considered. First, any record with missing data in a field needed for analysis was excluded. In the final model, this meant that 6% of the patient information was unaccounted for. Because of the large amount of data available, we did not think that imputing values was necessary or appropriate. Importantly, we do not believe that the loss of data was systematic, and therefore it is unlikely that this would bias our results. Second, all of the information in this study was based on a review of medical records for the index pregnancy. This includes information on clinical and obstetric history. As such, the possibility of misclassification for these variables exists. Again, we do not believe such misclassification would be systematic, and this would therefore bias our analysis towards the null. Third, there are some nonclinical factors that we did not have access to for this study, including 1) 24-hour anesthesia availability, 2) hospital-specific overall cesarean delivery rates, and 3) hospital delivery sizes. Thus, such factors could not be included as predictors in our analysis. We did include a "hospital" term in our analysis, so such characteristics are captured somewhat analytically. Fourth, we did not have specific information on the primary health care provider, and it is likely that there are provider characteristics (years since residency, site of residency training, malpractice history) that might impact the likelihood of a trial of labor. In addition, there might be interactions between provider factors, hospital factors, and patient factors that influence whether a patient has a trial of labor. Unfortunately, with this study design, we were unable to measure such provider factors.

Our study has several notable strengths as well. First, we have a large sample from which to draw our inferences. More importantly, we collected information from a mix of both community and tertiary care centers, making this study more generalizable than past work. Second, we collected information directly from patient records, rather than relying on information from birth certificates or other administrative data sets.

In conclusion, our study suggests that VBAC attempt rates vary widely by hospital independent of patient mix. In addition, patients with Medicaid insurance and black or Asian ethnicity have increased VBAC attempt rates relative to white patients. Given the known risks of VBAC, providers should be certain to adequately counsel all subpopulations considering VBAC.


   Footnotes
 
Supported, in part, by grants T32 HD 07440, R01 HD 35631, and K24 HD01289 (to GM) from the National Institutes of Health.

doi:10.1016/j.obstetgynecol.2003.08.010

Received March 27, 2003. Received in revised form July 23, 2003. Accepted August 15, 2003.


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ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
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