For women with a history of a prior cesarean delivery, planning mode of delivery for subsequent pregnancies involves careful consideration of several factors, including potential complications associated with repeat cesarean delivery compared with vaginal birth after cesarean (VBAC). While uterine rupture is arguably the most morbid of VBAC-associated morbidities, it occurs rarely.1,2 The precise incidence and risk for other morbidities associated with vaginal birth after cesarean delivery, such as bladder injuries, surgical complications, febrile morbidities, and need for blood transfusions, are less well-characterized. Specifically, the factors associated with bladder injury in this patient population are not well-established.
The published literature contains several case reports of uterine rupture with concomitant bladder injury or rupture.3–5 However, given that uterine rupture is not common, it is important for the obstetric surgeon to be aware of what other factors, if any, increase a patient’s risk for injury to the bladder. We undertook this study to estimate the incidence of and risk factors associated with bladder injury in patients with a history of a prior cesarean delivery.
MATERIALS AND METHODS
A multicenter retrospective cohort study of women with at least one prior cesarean delivery was conducted at 17 centers, both tertiary and community, in the northeastern United States between 1995 and 2000. Institutional review board approval was obtained for all 17 centers. The study was designed to estimate the incidence of maternal morbidities associated with vaginal birth after cesarean delivery and which factors were associated with these morbidities. The primary outcome for the initial cohort was symptomatic uterine rupture. In this secondary analysis, those patients who sustained a bladder injury were compared with those patients who did not sustain a bladder injury to estimate both the incidence of and the risk factors associated with bladder injuries of women with a history of at least one prior cesarean delivery. A detailed description of the large, retrospective cohort study has been published previously,2 but a brief description follows.
Patients were identified by International Classification of Disease, 9th Revision (ICD-9) codes for “previous cesarean delivery, delivered.” Data were extracted from medical records by trained research nurses using standardized, closed-end data collection forms. Reextraction of 3% of the medical records was used for quality assurance monitoring. Extensive information on maternal history and demographics, pregnancy, labor and delivery, and complications was obtained. Additionally, detailed information was collected on specific maternal morbidities, including bladder injury. Bladder injury was defined as any full-thickness injury to the bladder identified by the patient’s physician during their course of care and requiring repair. Charts were reviewed to distinguish full-thickness bladder injuries, which were the subject of this analysis, from incidental and less clinically relevant bladder injuries such as denuding of the bladder serosa. For this secondary analysis, the two study groups were defined by presence or absence of a bladder injury. The assessment of bladder injury risk factors was further stratified by planned delivery mode.
Descriptive statistics were used to estimate the incidence of bladder injury in patients with at least one prior cesarean delivery overall and by planned mode of delivery. The characteristics and birth outcomes of patients who sustained a bladder injury were compared with those who did not sustain one using Student t test, χ2, or Fisher exact test as appropriate. Stratified analysis was conducted to identify potential confounding variables. Finally, the results of the univariable and stratified analyses were used to select factors for our final multivariable models for bladder injury, stratified by planned mode of delivery. Backward selection was used to reduce the number of variables in the model by assessing the magnitude of change in the effect size of other risk covariates. Differences in the hierarchical explanatory models were tested using the likelihood ratio test or Wald test. All variables that were statistically significant, as well as those with known biologic importance or that were historically associated with VBAC morbidity and bladder injury, were included in the final models. Because hospital site was a potential confounder beyond the level of individual patient data and could have resulted in nonindependence within hospital groups, it was evaluated by cluster analysis in the final models. All statistical analyses were completed using Stata 8 software package Special Edition (StataCorp LP, College Station, TX).
Of 25,005 patients with at least one prior cesarean delivery, 107 (0.43%) sustained a bladder injury. Bladder injury risk was not affected by planned mode of delivery, with VBAC trial and elective cesarean delivery conferring similar risk (0.44% compared with 0.42%, adjusted odds ratio [OR] 1.36, 95% confidence interval [CI] 0.85–2.19). Of the 107 bladder injuries, 91.6% (n=98) occurred without concurrent uterine rupture.
The two study groups, those who experienced a bladder injury and those who did not, were compared on baseline characteristics (Table 1). The two groups were similar in many respects. There was no difference in gravidity, maternal race, gestational age at delivery, birth weight, or rate of comorbidities such as diabetes. There was also no difference in rates of acceptance to VBAC. The two groups differed slightly with regard to two measures. Women who experienced a bladder injury were 1 year older on average and were more likely to have had more than one prior cesarean delivery than the women who did not experience a bladder injury. In addition, patients with bladder injury seemed to have a higher rate of gestational hypertension compared with patients without bladder injury, but the difference did not reach statistical significance (P=.07).
When multivariable logistic regression was used to determine which factors were most strongly associated with bladder injury among patients who attempted VBAC (n=13,706), while adjusting for relevant confounding effects, a failed VBAC trial was significantly associated with more than a fourfold increased risk for bladder injury (0.86% compared with 0.22%, adjusted OR 4.61, 95% CI 2.70–8.11) (Table 2). Other established risk factors for VBAC failure and VBAC-associated morbidities were not significantly associated with bladder injury in the multivariable model, including number of prior hysterotomies, history of a prior vaginal delivery, delivery before 34 weeks gestation, induced (compared with spontaneous) labor, and African-American race (compared with white, Asian, or “other race”).
For patients who elected repeat cesarean delivery (n=11,299; Table 3), having more than one prior hysterotomy was the only significant factor independently associated with an increased risk of bladder injury (0.68% compared with 0.29%, adjusted OR 2.40, 95% CI 1.30–4.43). As in the model constructed for patients that attempted VBAC, other factors that have historically been associated with delivery-associated morbidities in VBAC candidates were not significantly associated with bladder injury in patients electing repeat cesarean delivery. The absolute risk of bladder injury in patients with a prior hysterotomy increased in the following ascending order: successful VBAC (0.2%), elective repeat cesarean delivery after one prior cesarean delivery (0.3%), elective repeat cesarean delivery after more than one prior cesarean delivery (0.7%), failed VBAC attempt (1.1%).
We found that the risk for bladder injuries in patients who have undergone a prior cesarean delivery is not related to planned mode of delivery. Interestingly, for patients undergoing a VBAC trial, more than 90% of bladder injuries occur without a concomitant uterine rupture. In fact, the most bladder injuries occur in the setting of a failed trial of labor. A heightened awareness by obstetricians of the increased risk of bladder injury during cesarean delivery for failed VBAC attempt could potentially reduce the rate of bladder injuries or reduce the risk of undiagnosed bladder injury in this patient population.
The potential for bladder injury is not foreign to obstetricians. Injury to the bladder has been reported at rates of approximately 0.1 per 1,000 births,6 and 3.1 per 1,000 cesarean deliveries.7 Recently, Phipps and colleagues8 performed a nested case–control study within a retrospective cohort of women undergoing cesarean delivery to identify factors associated with the risk of bladder injury. They found bladder injury occurred in 0.28% of more than 14,000 deliveries and identified a few factors associated with bladder injuries at the time of cesarean delivery, including prior cesarean delivery (adjusted OR 3.82, 95% CI 1.62–8.97). However, clinical details needed to characterize the association fully were not available for the subgroup of patients with a prior hysterotomy.
Our study allowed a more precise estimate of the risk of bladder injury in patients who had undergone a prior cesarean delivery. Additionally, our study design enabled us to assess different risk factors associated with bladder injury in patients who underwent a trial of labor or elected a repeat cesarean delivery. Recently published data by Alexander et al9 helps put this risk in context. They compared maternal and fetal outcomes of women who underwent a primary cesarean delivery during the first stage of labor with those of women who underwent cesarean delivery in the second stage of labor. Of the several intraoperative complications studied, bladder injury was one of them. The investigators found that 0.4% of the 2,716 women who had a cesarean delivery during the second stage of labor sustained a bladder injury as compared with 0.1% of women who had a cesarean delivery during the first stage of labor. The elevated risk of cystotomy in patients undergoing cesarean delivery after complete cervical dilation found by Alexander and colleagues is similar to the risk of cystotomy in our VBAC study. These investigators were not able to comment on specific factors associated with risk of bladder injury, and their results are not necessarily generalizable to VBAC candidates, because the study population included only patients undergoing primary cesarean delivery. Thus our study complements theirs, and we were able to determine that the dominant risk factors for cystotomy in patients with a prior cesarean delivery were having a failed VBAC attempt and the number of prior hysterotomies.
Our study offers several strengths. The large sample size allowed us to study a relatively rare outcome, which has limited other authors in their ability to comment on risk associated with bladder injury in this patient population. The robust information on patients in the cohort, including history, demographics, and pregnancy course, allowed us to test the association of several factors with the risk of bladder injury, while adjusting for known potentially confounding effects. Conversely, there were some study weaknesses that should be considered. We were not able to adjust for individual operator factors, such as the surgeon’s level of experience. However, we did account for surrogate markers, such as delivery site and whether a particular institution had an obstetric residency training program. Additionally, it is possible that the bladder injury risk may be associated with the indication or urgency of the cesarean delivery, but we were not able to evaluate cesarean delivery indication because the information was not available. Two additional potential weaknesses are worth noting. First, there is potential for ascertainment bias. That is, for women who did not deliver by cesarean, it is possible that they experienced a bladder injury that went undetected because they did not undergo a laparotomy. However, we would offer that these injuries may not have clinical significance because, by definition, they go undetected because patients are asymptomatic. Finally, the retrospective nature of the study design introduces the potential for selection bias, because patients were not randomly assigned to mode of delivery. However, given good clinical practice, the existence of this would most likely bias the results toward the null. Despite these limitations, we feel our findings are valid and clinically important.
For patients who have had at least one prior cesarean delivery, the risk of bladder injury at subsequent delivery is relatively infrequent and not related to mode of delivery. Contrary to case reports of uterine rupture with concomitant bladder injury, which suggests that most bladder injuries in patients attempting VBAC happen in the setting of uterine rupture, the overwhelming majority of bladder injuries in VBAC candidates occur in the absence of uterine rupture. For patients attempting VBAC, the majority of bladder injuries occur in the setting of a failed VBAC. Similar to the findings by Silver and colleagues,10 an increasing number of prior cesarean deliveries seems to increase the risk for bladder injury in patients electing repeat cesarean delivery. We believe these data will help heighten physician awareness of the increased risk for bladder injury when performing a cesarean delivery in the setting of a failed VBAC attempt or elective repeat cesarean delivery.
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