Uterine Rupture During VBAC Trial Of Labor: Risk Factors and Fetal Response

The Effect of Labor on Uterine Rupture

Three large population-based, cohort analyses have demonstrated that the risk for uterine rupture exists, whether a woman with a prior cesarean birth has a scheduled repeat cesarean or VBAC-TOL ( Table 2 ). Gregory et al.^[26] reviewed California hospital discharge summary data for 1995 and reported a uterine rupture rate of 0.28% (n = 79/27,760) among women who elected repeat cesarean without labor and a rate of 0.53% (209/39,096) among women who underwent VBAC-TOL. Rageth et al.^[10] examined a database of records from 17,613 women attempting VBAC-TOL in Switzerland and reported an overall uterine rupture rate of 0.4% (n = 70/17,613) in the VBAC-TOL group, which was slightly higher than the 0.19% uterine rupture rate in the women who underwent elective repeat cesarean birth (n = 22/11,433). Similarly, Lydon-Rochelle et al.^[12] reviewed Washington State vital records and abstracted hospital discharge (ICD-9) diagnoses to report a 0.16% (n = 11/6,980) incidence of uterine rupture among women who underwent an elective repeat cesarean without labor and an incidence of uterine rupture of 0.6% (n = 80/13,115) among women attempting VBAC-TOL. In each of these population-based studies, the effect of labor appears to increase the incidence of uterine rupture in women who underwent VBAC-TOL. However, it is unclear whether this increased incidence of uterine rupture is secondary to other risk factors, specifically the additive effect of induction of labor with either oxytocin and/or prostaglandins.

Labor Induction and Augmentation With Oxytocin

Two large population-based studies have evaluated the effect of oxytocin induction and/or augmentation on uterine rupture during TOL. In a study by Rageth et al.,^[10] 17,613 women underwent VBAC-TOL in which 70 women experienced uterine rupture. Women in the uterine rupture group had increased rates of induced labor (24%) compared to the women in the non-rupture group (13.9%) (P = .013). Similarly, Lydon-Rochelle et al.^[12] found women who experienced spontaneous labor had a 0.52% (n = 56/10,789) incidence of uterine rupture compared to an incidence of 0.77% (n = 15/1,960) in women whose labors were induced with oxytocin.

Few studies separately evaluate the effects of oxytocin induction versus oxytocin augmentation on uterine rupture during TOL. Zelop et al.^[44] reported a uterine rupture rate of 0.7% (n = 16/2,214) among women attempting VBAC-TOL with spontaneous labor compared to 2.0% (n = 9/458) among women induced with oxytocin. After controlling for birth weight, epidural anesthesia, duration of labor, maternal age, year of delivery, and years since last birth, induction of labor with oxytocin was associated with a 4.6-fold increased risk of uterine rupture, compared to the rate noted in women who had spontaneous labor (OR: 4.6; 95% CI: 1.5-14.1). Augmentation with oxytocin was found to be associated with a 2.3-fold increased risk of uterine rupture (OR: 2.3; 95% CI: 0.8-7.0); however, this difference was not statistically significant.

Leung et al.^[45] conducted a case-control study of 70 women with prior cesarean birth attempting VBAC-TOL. After controlling for confounding variables, women receiving oxytocin were almost 3 times more likely to experience uterine rupture than the women in the control group (OR: 2.7; 95% CI: 1.2-6.0). Dysfunctional labor had an even greater effect on increasing the incidence of uterine rupture. Dysfunctional labor, primarily arrest disorders, increased the risk of uterine rupture 7-fold (OR: 7.2; 95% CI: 2.7-20.0). However, a majority of the women who received oxytocin also experienced dysfunctional labor. The presence of dysfunctional labor may be a factor for uterine rupture or a marker for its occurrence. Further study is needed to determine if the major risk for uterine rupture is dysfunctional labor, use of oxytocin, or both.

In summary, studies performed to date suggest oxytocin use may result in a higher risk of uterine rupture during VBAC-TOL. Therefore, it is prudent to exercise caution when inducing or augmenting labor in a woman with a scarred uterus. Labor progression must be carefully followed and the woman and her fetus must be monitored closely in an institution capable of immediate emergency response.^[13]

Labor Induction With Prostaglandins

Two types of prostaglandin agents are currently used for cervical ripening and labor induction: prostaglandin E2 (Prepidil, Cervidil) and the analogue of prostaglandin E1, misoprostol (Cytotec). The use of prostaglandin E2 (PGE2) gel in women with previously scarred uteri is associated with a clear increased incidence of uterine rupture. However, in several of the initial studies, it is unclear whether the cases of uterine rupture were related to PGE2 gel alone or to PGE2 gel in combination with oxytocin administration.^[46,47]

Zelop et al.^[44] examined the effects of PGE2 gel on women who underwent VBAC-TOL. Among the 35 women in whom labor was induced by PGE2 alone, uterine rupture occurred in 2.9% (n = 1/35) compared to 4.5% (n = 3/67) among the 67 women who received both PGE2 and oxytocin for induction ( Table 3 ). Overall, the rate of uterine rupture among those who received any PGE2 gel was 3.9% compared to 0.9% among those who did not receive PGE2 gel (P = .02). However, 84 of the 102 women who received PGE2 gel also received oxytocin. After controlling for oxytocin induction and augmentation, birth weight, use of epidural anesthesia, duration of labor, maternal age, year of delivery, and years since last birth, induction of labor with PGE2 gel alone was not found to be a significant risk factor for uterine rupture. Although the odds ratio of 3.2 (95% CI: 0.9-10.9) suggests an association, it is not statistically significant.

The recent population-based, retrospective analysis by Lydon-Rochelle et al.^[12] noted a significant increase in the incidence of uterine rupture in women who underwent VBAC-TOL and were induced with prostaglandins. Uterine rupture occurred at a rate of 1.6 per 1,000 women who experienced a repeat cesarean birth without labor compared to an incidence of 24.5 per 1,000 women in the induction of labor with prostaglandins group (RR: 15.6; 95% CI: 8.1-30.0). Although the authors concluded that induction of labor with prostaglandins significantly increases the risk of uterine rupture among women with a previous cesarean birth, they did not have information on specific types and dosages of prostaglandins used. The authors acknowledged that their use of ICD-9 codes might have caused an overstatement of the actual incidence of uterine ruptures, secondary to the use of a single ICD code for both uterine incision extension and uterine rupture.

Misoprostol

Misoprostol (prostaglandin E1) is gaining popularity as an option for cervical ripening and labor induction in women without previous uterine surgery. A number of studies have found the use of misoprostol to be a significant risk factor for uterine rupture in women with a prior cesarean birth.^{[48,49,50,51,52,53,54]} However, some of the studies evaluating misoprostol in women who undergo VBAC-TOL are confounded by concomitant use of oxytocin. The definitive work in this area was a randomized controlled trial conducted by Wing et al.^[50] Women were originally randomized to 25 mcg of misoprostol intravaginally every 6 hours to a maximum of four doses, or to intravenous oxytocin per a standard infusion protocol. Seventeen women received misoprostol and 21 women received oxytocin. The study was stopped prematurely secondary to two emergency cesarean sections with noted uterine disruption at the time of surgery in the women who received misoprostol. In a larger series, Plaut et al.^[52] reviewed the uterine rupture cases from two hospitals over 20 months in 1996 to 1997. Of the 89 women induced with misoprostol in this combined series, uterine rupture occurred in 5.6% (5/89).

No studies or metanalyses have been conducted that have large enough numbers to detect a statistically significant relationship between misoprostol use and uterine rupture during VBAC-TOL. A recent COCHRANE review^[55] evaluated 62 trials in which vaginal misoprostol was used for cervical ripening or induction of labor in women with unscarred uteri. The review concluded that the studies were not large enough, either individually or cumulatively, to exclude the possibility of uterine rupture. In April 2002, the ACOG issued a committee opinion that discourages the use of prostaglandins for cervical ripening or induction of labor in women attempting VBAC-TOL.^[56] ACOG supports the practice of VBAC-TOL under proper circumstances and with appropriate safeguards.^[13,56]

J Midwifery Womens Health. 2003;48(4) © 2003  Elsevier Science, Inc.

Cite this: Uterine Rupture During VBAC Trial Of Labor: Risk Factors and Fetal Response - Medscape - Jul 01, 2003.