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Risk Factors for Bladder Injury During Cesarean Delivery

Maureen G. Phipps, MD, MPH^*, Bryan Watabe, MD^*, Jeffrey L. Clemons, MD, Sherry Weitzen, PhD^* and Deborah L. Myers, MD^*

From the *Departments of Obstetrics and Gynecology and Community Health, Brown Medical School, Providence, Rhode Island; Women and Infants Hospital, Providence, Rhode Island; and Department of Obstetrics and Gynecology, Madigan Army Medical Center, Tacoma, Washington.

Address reprint requests to: Maureen G. Phipps, MD, MPH, Women and Infants Hospital, 101 Dudley Street, Providence, RI 02905; e-mail: mphipps{at}wihri.org.

	ABSTRACT

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
OBJECTIVE: During the period of this research, M.G.P. was supported by the Building Interdisciplinary Research Careers in Women's Health (BIRCWH) program (K12 HD43447-01) of the National Institutes of Health.

To identify risk factors for bladder injury during cesarean delivery so as to inform patients and practitioners of these risks.

METHODS: We conducted a case-control study of women undergoing cesarean delivery at Women and Infants Hospital between January 1995 and December 2002. Cases were women with bladder injuries at the time of cesarean delivery. Two controls per case were selected randomly. Medical records were reviewed for demographic and clinical data to compare cases and controls.

RESULTS: Forty-two bladder injuries were identified among 14,757 cesarean deliveries (incidence of 0.28%). Prior cesarean delivery was more prevalent among cases than controls (67% versus 32%, P < .01). The adjusted risk for bladder injury associated with prior cesarean delivery was 3.82 (95% confidence interval 1.62–8.97). Statistically significant differences (P values .01) between cases and controls were found in emergent timing of delivery (31% versus 11%), labor before cesarean (83% versus 61%), attempted vaginal birth after cesarean (64% versus 22%), concurrent uterine rupture (14% versus 0%), adhesions (60% versus 10%), age (33.6 versus 29.3 years), and body mass index (29.9 versus 33.0 kg/m²). No differences were found among type of uterine incision, labor induction, chorioamnionitis, fetal position, gestational age, or maternal illnesses.

CONCLUSION: Prior cesarean delivery is a risk factor for bladder injury at the time of repeat cesarean delivery. Patients should be counseled regarding this risk, particularly in the setting of increasing rates of elective primary cesarean delivery.

LEVEL OF EVIDENCE: II-2

Nielsen and Hokegard⁴ evaluated overall surgical complications in 1,319 cesarean deliveries. They found most complications occurred during emergency cesarean delivery and that, during emergency cesarean delivery, 6 factors were associated with increased complications: station before surgery, labor before surgery, low gestational age (< 32 weeks), rupture of chorionic membranes before surgery, prior cesarean delivery, and skill of operator.

The literature concerning bladder injury at the time of cesarean delivery is limited to a few case series (MEDLINE search 1966–2003).^5–9 The reported incidence of bladder injury with cesarean delivery ranges from 0.14%⁵ to 0.94%.⁶ The largest series of 23 bladder injuries, reported by Eisenkop et al⁷ in 1982, demonstrated an overall incidence of 0.31%, with an incidence of 0.19% in primary cesarean deliveries and 0.6% in repeat cesarean deliveries.

Although intuitive to many practitioners, the risk for bladder injury during cesarean delivery has not been adequately investigated. As the rate of cesarean delivery rises, it is important to identify risk factors for bladder injury based on evidence so as to help practitioners counsel their patients. Specific risk factors for bladder injury during cesarean delivery have not been reported in the above studies. Because Women and Infants Hospital performs approximately 9,000 deliveries per year, with a cesarean rate of approximately 21%, it is an ideal setting to study this uncommon outcome. The purpose of our study was to identify risk factors for bladder injury during cesarean delivery in order to inform patients and practitioners of these risks.

	MATERIALS AND METHODS

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We performed an institutional review board–approved, case-control study of women undergoing cesarean delivery at Women and Infants Hospital between January 1995 and December 2002. Among the 70,800 deliveries at Women and Infants Hospital during this study period, 14,757 cesarean deliveries were performed. All women undergoing cesarean delivery during the study period were eligible for inclusion. Cases and controls were identified through the Women and Infants Hospital health information database system. Cases were defined as women whose Current Procedural Terminology codes identified them as having bladder injuries at the time of cesarean delivery (codes 57.81 and 75.61). Two controls per case were identified by randomly selecting 2 women undergoing cesarean delivery on the same day as each case. A random numbers table was used for selecting the controls based on the patient medical record number.

The medical records for cases and controls were reviewed. Demographic and background data collected included age, race, parity, gestational age, body mass index, and medical provider (private, clinic, or maternal–fetal medicine service). Surgical history included the number of prior cesarean deliveries and any prior pelvic surgery. Information collected about the cesarean delivery included indication for cesarean delivery, attempted vaginal birth after cesarean (VBAC) in those with a prior cesarean delivery, type of uterine incision, timing of delivery (elective, urgent, or emergent), and concurrent uterine rupture. Timing of delivery was defined as 1) elective, if the surgery was scheduled, 2) urgent, if surgery needed to be performed in a timely manner but not as an immediate emergency delivery, or 3) emergent. Characteristics of labor and delivery collected included the presence of labor before cesarean, rupture of chorionic membranes, station of the presenting fetal part, fetal position, presence of chorioamnionitis, and induction of labor. Information about the infant, including birth weight and Apgar scores, was also obtained. Operative information collected about the cesarean delivery included the estimated blood loss, presence of adhesions, and time between skin incision and uterine incision. For bladder injury cases, information about the cystotomy was collected, including injury location, time of recognition, time of injury (if known), size of injury, presence of ureteral injury, need for stent placement, and type of repair performed.

A power analysis was performed based on the incidence of bladder injury reported in the literature for primary and repeat cesarean deliveries. Using an alpha of 0.05, a power of 80%, and a ratio of 1 case to 2 controls, we determined that to demonstrate a 3-fold increased risk for bladder injury among women who had a prior cesarean delivery compared with those who did not have a prior cesarean delivery, would require approximately 40–45 cases and 80–90 controls. The Statcalc function from EpiInfo 2000 (Centers for Disease Control and Prevention, http://www.cdc.gov/epiinfo/) was used to perform the power analysis.

The data were analyzed using ² test or Fisher exact test to compare categorical variables and 2 sample t tests to compare continuous variables. Because of multiple comparisons being made, we used a P value of .01 as meaningfully statistically significant. Logistic regression was used to further assess the association between the risk for bladder injury and prior cesarean delivery, controlling for potential confounders. Odds ratios (ORs) and 95% confidence intervals (CIs) were computed. A subgroup analysis excluding those attempting to have a VBAC was also performed. STATA 8.0 (College Station, TX) was used for the statistical analysis.

	RESULTS

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Between January 1995 and December 2002, 14,757 cesarean deliveries were performed at Women and Infants Hospital. Of these, 9,723 were primary cesareans deliveries and 5,034 were repeat cesareans deliveries. A total of 42 cases of bladder injury were identified, for an overall incidence of bladder injury of 0.28% (42/14,757). Of these, 28 of 42 occurred in repeat cesarean deliveries (incidence of 0.56%), and 14 of 42 occurred in primary cesarean deliveries (incidence of 0.14%).

Differences between cases and controls were noted among several demographic and background characteristics (Table 1). Women with bladder injury (cases) were older than controls (33.6 versus 29.3 years). Cases also had a lower body mass index (29.9 versus 33.0 kg/m²) and greater parity (79% versus 52% parous) than controls. There were no other significant differences in background characteristics between cases and controls.

Women with a bladder injury (cases) were more likely to have had a prior cesarean delivery compared with the control group (67% versus 32%). Cases were also more likely than controls to have had prior pelvic surgery. Presence of adhesions during the procedure was greater in the bladder injury group than in controls (60% versus 10%).

Labor and delivery characteristics were compared between the groups (Table 2). The presence of labor was more common among women with a bladder injury than controls (83% versus 61%). Labor characteristics approached significance (P = .03), including rupture of membranes and fetal station.

The timing of delivery differed significantly between the groups. Women with a bladder injury were more likely to undergo emergent delivery (31% versus 11%) or urgent delivery (62% versus 55%) than controls and less likely than controls to have a scheduled delivery (14% versus 27%). Regarding indication for cesarean delivery, arrest of descent was more frequent among cases (36% versus 11%, P < .01), and breech was less frequent among cases (2.4% versus 19%, P = .01) when compared with controls. Among those with a prior cesarean delivery, attempted VBAC with trial of labor was more common among the bladder injury group than the controls (64% versus 22%). The presence of uterine rupture at the time of surgery was also more frequent in the bladder injury group than the controls (14% versus 0%). The type of uterine incision did not differ between the 2 groups, and none of the patients required a cesarean hysterectomy. The estimated blood loss was greater in the bladder injury group (1,083 versus 626 mL). Additionally, among the 42 bladder injury cases, 13 occurred during an emergent delivery, and 62% (8 of 13) of those patients had a prior cesarean delivery. None of the patients undergoing emergent deliveries in the control group (9 of 84) had a history of a prior cesarean delivery. Infant characteristics were similar between the groups, including birth weight (3,426 versus 3,113 g, P = .06), 1- and 5-minute APGAR scores, and arterial cord blood pH.

To assess the association between the risk for bladder injury and prior cesarean delivery and the influence of other factors, logistic regression was performed. Results from the simple logistic model indicate that women who had prior cesarean delivery were 4.22 times as likely to develop a bladder injury at delivery as women who had not had a prior cesarean delivery (crude OR 4.22, CI 1.79–10.1). Although we considered the other apparent risk factors for bladder injury, such as age, parity, body mass index, adhesions, labor, rupture of membranes, station, timing of delivery, time from skin incision to uterine incision, and estimated blood loss, in sequential regression models, only age and body mass index were confounders for the relationship between prior cesarean delivery and bladder injury. After adjusting for age and body mass index, the risk for bladder injury associated with prior cesarean delivery continued to be elevated, with an odds ratio of 3.82 (95% CI 1.62–8.97).

To explore the association of attempted VBAC with risk of bladder injury, a subgroup analysis was performed that excluded cases and controls who had attempted VBAC. The odds ratio for the risk of bladder injury associated with prior cesarean delivery among the remaining 24 cases and 78 controls is 1.94 (95% CI 0.66–5.33).

Within the bladder injury group, data were collected on the characteristics of the injury and the types of repair. Of the injuries, 40 of 42 cases (95%) occurred in the dome of the bladder, and 3 of 42 cases (7%) involved the trigone. Four cases required ureteral stenting, of which one was a direct ureteral injury. The length of the bladder injuries ranged from 1 to 10 cm, with a mean of 4.2 cm. The timing of the bladder injury was reported in 21 (50%) of the cases: 7 (33%) occurred during entry into the peritoneal cavity, 9 (43%) occurred during creation of the bladder flap, and 5 (24%) occurred during the uterine incision or delivery. The recognition of the bladder injury usually occurred after delivery of the infant and repair of the uterine incision, 26 of 42 (62%). Among the remaining bladder injuries, 5 (12%) were recognized during entry into the peritoneal cavity, 9 (21%) during creation of the bladder flap, and 2 (5%) before closing the abdomen. All bladder injuries were recognized before leaving the operating room.

	DISCUSSION

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
The cesarean delivery rate has been rising over the past several years.¹⁰ This rise in cesarean deliveries has garnered attention and concern in the lay press as well as the medical literature.¹¹ There is disagreement as to whether it is good for the cesarean delivery rate to be rising and if there is a "right" cesarean delivery rate that should be targeted. Some authors have suggested performing elective primary cesarean deliveries,^12–15 and The American College of Obstetricians and Gynecologists recently released a Committee Opinion defending the ethics of offering primary elective cesarean deliveries in informed patients.¹⁶ The increase in primary cesarean deliveries will unavoidably lead to an increase in the number of repeat cesarean deliveries. With an increasing cesarean delivery rate, the number of complications, including bladder injuries, can be expected to rise.

Our data suggest that a prior cesarean delivery is a significant risk factor for bladder injury occurring at the time of a cesarean delivery, conferring a 4-fold increased risk over a primary cesarean delivery. The data further suggest that adhesions from a prior cesarean delivery increase the risk of a bladder injury at the time of cesarean delivery. Other prior pelvic surgery also represents a risk factor for bladder injury at the time of cesarean delivery, and the presence of adhesions was greater when bladder injury occurs. In particular, adhesion formations between the bladder and the lower uterine segment are a likely causative factor, because 43% of bladder injuries occurred during formation of the bladder flap. This is consistent with the findings of Eisenkop et al.⁷

Bladder injuries are also more likely to occur in older and more parous women. This finding may reflect that women undergoing a repeat cesarean delivery are likely to be older and more parous than those undergoing a primary cesarean delivery. Interestingly, cases had a lower body mass index than controls in this study. After adjusting for the effects of age and body mass index, the risk of bladder injury associated with prior cesarean delivery remained statistically significant, with a nearly 4-fold increased risk.

Emergency cesarean delivery was found to be a significant risk factor for bladder injury, which is consistent with the findings of Rajasekar and Hall.⁵ Injury occurred during entry into the peritoneal cavity in 33% of bladder injuries. This likely represents the stressful nature of an emergency delivery, including the creation of a bladder flap in an emergency or a need to perform a uterine incision without a bladder flap, which places the bladder at risk for injury. Furthermore, for those women undergoing an emergent cesarean delivery, having a prior cesarean delivery was more common in the bladder injury group, which may be a consequence of scar tissue and the challenging nature of the surgery.

Labor is also found to be a significant risk factor for bladder injury during a cesarean delivery. To determine the effect of labor on the association of prior cesarean delivery with bladder injury, we included labor in our regression model, but a meaningful odds ratio was not obtainable because there were no cases that did not have either a prior cesarean delivery or labor. We attempted to account for labor in women with prior cesarean deliveries by repeating the analysis, but excluding women attempting a vaginal birth after cesarean. The resulting odds ratio of 1.94 was not statistically significant. The decrease in the risk among these women compared with the full sample may suggest an increased risk attributable to labor after a prior cesarean, and possibly labor in general, and the resulting lack of significance may be due to the decreased sample size

This is a large observational study assessing the risk for bladder injury during cesarean delivery. We do recognize several limitations to this study, including that bladder injuries may be grossly underreported in the medical records. Bladder injuries may not be recognized as significant during the case. Relying on medical coding to identify our cases initially, which depends on the practitioner writing the injury in the medical record and the record analyst coding it correctly, may also be problematic. Moreover medical record review also brings out inherent bias in reporting on risk factors and confounding variables. Considering these scenarios, the speculation of these authors is that, if all bladder injuries were reported accurately, there would be a more significant association of bladder injury with prior cesarean delivery. The magnitude of this association is unclear.

Because the indications for cesarean delivery are widening and because primary elective cesarean delivery is gaining acceptance in the public and among providers, it is important that we study and understand the complications associated with cesarean delivery and, particularly, with repeat cesarean delivery. Bladder injury is one such complication that occurs during cesarean delivery, and as we have shown here, a prior cesarean delivery represents a significant risk factor for a bladder injury occurring during cesarean delivery. Women requesting primary cesarean deliveries should be counseled about the potential for significant surgical complications in repeat cesarean deliveries when discussing the indications for a primary elective cesarean delivery.

	Footnotes

 
The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Department of the Army or the Department of Defense.

During the period of this research, M.G.P. was supported by the Building Interdisciplinary Research Careers in Women's Health (BIRCWH) program (K12 HD43447-01) of the National Institutes of Health.

Received August 2, 2004. Received in revised form September 21, 2004. Accepted September 29, 2004.

doi:10.1097/01.AOG.0000149150.93552.78

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