Objective
We sought to characterize the labor of women attempting trial of labor after cesarean (TOLAC) who experience uterine rupture.
Study Design
We conducted a secondary analysis of a nested case-control study of women attempting TOLAC. Women experiencing uterine rupture (cases) were compared to 2 reference groups: successful TOLAC and failed TOLAC. Interval-censored regression was used to estimate the median time to progress 1 cm in dilation and the total time from 4-10 cm.
Results
A total of 115 cases were compared to 341 successful TOLAC and 120 failed TOLAC. The time to progress 1 cm was similar between groups until 7-cm dilation. After 7 cm, cases of uterine rupture required longer to progress than successful TOLAC (median [95th percentile] time from 7-8 cm: 0.38 [1.91] vs 0.16 [0.79] hours; from 8-9 cm: 0.28 [1.10] vs 0.10 [0.39] hours). Women with a uterine rupture had labor curves similar to those with a failed TOLAC.
Conclusion
Women with labor dystocia in the active phase of labor should be closely monitored for uterine rupture in TOLAC.
Although trial of labor after cesarean (TOLAC) is considered an appropriate option in women with a prior low transverse cesarean, uterine rupture is a potentially devastating event that occurs in <1% of attempts. Several signs of uterine rupture have been identified, including nonreassuring fetal heart rate, loss of station, maternal pain, and maternal hemodynamic instability; however, a uterine rupture would ideally be diagnosed prior to the occurrence of maternal or fetal compromise.
Some have proposed that labor dystocia is a risk factor for uterine rupture as a result of prolonged exposure of the hysterotomy scar to uterine contractions. Unfortunately, the clinical course of labor leading up to uterine rupture has only rarely been described. Such information may aid in the management of labor in women with a prior cesarean. Therefore, we sought to characterize the pattern of labor in TOLAC associated with uterine rupture. Additionally, we compared the pattern of labor observed in women who experienced a uterine rupture with 2 reference groups: those who had a successful TOLAC and those who had a failed TOLAC.
Materials and Methods
This was a secondary analysis of a nested case-control study conducted from 1996 through 2000 within a 17-center retrospective cohort study of pregnant women with at least 1 previous cesarean delivery. For the original study, to identify factors associated with uterine rupture, all cases (women who attempted TOLAC and experienced uterine rupture) were matched on hospital site with 5 control subjects, chosen by a random number generator, who attempted TOLAC but did not suffer a uterine rupture. Institutional review board approval was obtained from all study sites. A detailed description of the parent study has been published previously, but a brief description follows.
International Classification of Diseases, Ninth Revision , codes for “previous cesarean delivery, delivered,” were used to identify subjects at each site and data were extracted from the paper-charted medical charts by trained research nurses using standardized, closed-end data collection forms. Of charts, 3% were re-extracted for quality control. Data collected included maternal demographics, medical and obstetric history, antepartum course, labor and delivery events, complications, and maternal outcomes. Data for patients selected for the case-control study were re-extracted in further detail, including all procedures, medications, and examination details in 15-minute time increments throughout labor. Only women with ≥1 low transverse cesareans were included in the parent cohort; patients were excluded if their prior cesarean was not low transverse.
Uterine rupture was explicitly defined a priori as a full-thickness disruption of the uterine wall accompanied by at least one of the following clinical signs: nonreassuring fetal heart rate tracing immediately preceding surgery, hemoperitoneum identified intraoperatively, or signs of maternal hemorrhage (systolic blood pressure <70 mm Hg, diastolic blood pressure <40 mm Hg, or heart rate >120 beats/min). This definition was used to distinguish a clinically significant uterine rupture from an asymptomatic or incidental finding of uterine scar separation or “uterine window.”
For this analysis, subjects were included if they delivered at ≥37 weeks and at least 2 time points in their labor course were known (ie, 1 cervical examination and time of complete dilation). Two reference groups were formed. The first reference group was composed of women with a successful TOLAC (women who reached 10 cm and delivered vaginally) to provide a reference for a normal TOLAC. However, it is impossible to predict at the beginning of labor who will have a successful TOLAC and it is unclear what impact a failed TOLAC will have on labor curves. Therefore, a second reference group composed of women with a failed TOLAC (women who attempted a TOLAC but had a repeat cesarean) was used.
The 3 groups were compared with respect to baseline characteristics: χ 2 or Fisher exact tests, as appropriate, for dichotomous variables and analysis of variance or Mann-Whitney U test, as appropriate, for continuous variables. Additionally, a sensitivity analysis of sociodemographics was performed, comparing the controls used for this analysis with the group of patients who did not experience a uterine rupture in the larger cohort to ensure that the controls chosen at random were representative of the entire cohort (data available upon request: harperl@wudosis.wustl.edu ). Because controls for this analysis were representative of the larger cohort, weights for the final covariates were not used.
We analyzed the median time required for cervical dilation to progress from 4-10 cm in aggregate as well as by increments of 1 cm (eg, from 3-4 cm). It is not possible to know the exact time that a level of cervical dilation is attained due to the variability of cervical dilation at first examination and subsequent timing of examinations. Thus, we calculated a minimum and maximum time interval between each centimeter of cervical dilation that was reached. We calculated the time interval between each consecutive cervical dilation for all individuals giving them an interval-censored value for each level of dilation. The time interval assumption fits a log normal distribution, and previous publications have demonstrated that the duration of labor often has a right-skewed pattern. We used PROC LIFEREG of SAS 9.2 (SAS Institute Inc, Cary, NC) to fit a log normal distribution to the time interval and estimated median, fifth, and 95th percentiles. Multivariate models were built to adjust for relevant confounding factors. Variables demonstrated to be historically relevant (prior vaginal delivery) as well as those identified in bivariable analyses (induction of labor, oxytocin use) were considered and selected based on the Wald χ 2 statistic using a P value of .1. These analyses were repeated to stratify by prior vaginal delivery, as well as by labor type (induced vs spontaneous).
Results
Within the retrospective cohort of 25,005 patients with a history of at least 1 prior cesarean delivery, 13,706 attempted TOLAC, and, of those, 134 experienced a uterine rupture (cases). At random, 659 of the 13,706 patients who attempted TOLAC but did not experience a uterine rupture were selected as controls. Of these 659 controls, 341 women had a successful TOLAC and 120 had a failed TOLAC and met inclusion criteria for this analysis (70 excluded for preterm delivery, 128 for <2 time points). Of the 134 subjects experiencing uterine rupture, 115 cases met inclusion criteria for this analysis (7 excluded for preterm delivery, 12 for <2 time points). Cases and controls were similar with respect to age, gravidity, epidural use, diabetes, hypertension, type of hospital, birth weight, and gestational age at delivery. Cases were more likely to have been induced or have received oxytocin; cases were less likely to be black or to have had a prior vaginal delivery ( Table 1 ) .
| Characteristic | Uterine rupture (n = 115) | Successful TOLAC (n = 341) | Failed TOLAC (n = 120) | P value |
|---|---|---|---|---|
| Age, y | 31.7 ± 5.1 | 30.7 ± 5.4 | 30.6 ± 6.0 | .19 |
| Gravidity | 3.1 ± 1.4 | 3.3 ± 1.6 | 3.5 ± 1.6 | .11 |
| Prior vaginal delivery | 17 (16.4%) | 115 (34.7%) | 44 (38.6%) | < .01 |
| Black race | 32 (27.8%) | 122 (35.8%) | 59 (49.2%) | < .01 |
| Epidural | 103 (89.6%) | 284 (83.3%) | 95 (79.2%) | .09 |
| Diabetes | 4 (3.9%) | 12 (3.6%) | 6 (5.3%) | .74 |
| Hypertension | 5 (18.9%) | 9 (2.7%) | 4 (3.5%) | .57 |
| University hospital | 52 (60.5%) | 195 (67.5%) | 73 (69.5%) | .38 |
| Labor induction | 48 (46.2%) | 96 (29.0%) | 52 (45.6%) | < .01 |
| Prostaglandins | 28 (24.4%) | 20 (5.9%) | 13 (10.8%) | < .01 |
| Oxytocin (any) | 70 (67.3%) | 137 (41.4%) | 52 (45.6%) | < .01 |
| Oxytocin augmentation (not induced) | 34 (29.6%) | 77 (22.6%) | 24 (20.0%) | .37 |
| No. of vaginal examinations, Median (interquartile range) | 5 (4-6) | 5 (4-7) | 5 (3-6) | .39 |
| Birthweight, g | 3550 ± 501 | 3729 ± 1183 | 3763 ± 1152 | .26 |
| Gestational age at delivery, wk | 39.3 ± 1.3 | 39.2 ± 1.2 | 39.6 ± 1.3 | .03 |
Table 2 displays the number of subjects in the uterine rupture and failed TOLAC groups who reached a given dilation. This table is displayed because subjects could only be included in the interval-censored regression if they reached the maximum dilation being studied. For example, of the 115 women with uterine rupture, 29 (25.2%) reached 10 cm and were included in the analysis from 9-10 cm.
| Maximum dilation, cm | No. of patients with uterine rupture | No. of patients with repeat cesarean |
|---|---|---|
| 1 | 5 | 5 |
| 2 | 7 | 8 |
| 3 | 7 | 17 |
| 4 | 12 | 11 |
| 5 | 14 | 16 |
| 6 | 15 | 23 |
| 7 | 3 | 12 |
| 8 | 9 | 15 |
| 9 | 14 | 13 |
| 10 | 29 | 0 |
After adjusting for prior vaginal delivery, the median for the overall length of time spent in labor (from 4-10 cm) was similar between those who experienced a uterine rupture and the 2 reference groups ( Table 3 ). The time spent progressing each 1 cm of dilation is similar between the uterine rupture group and the failed TOLAC group; the labor patterns of these 2 groups cannot be distinguished.
| Cervical dilation, cm | Successful TOLAC (n = 341) | P value a | Uterine rupture (n = 115) | P value b | Failed TOLAC (n = 120) |
|---|---|---|---|---|---|
| 3-4 | 0.63 (0.13, 3.11) | .46 | 0.48 (0.10, 2.37) | .26 | 0.48 (0.16, 3.81) |
| 4-5 | 0.48 (0.09, 2.63) | .53 | 0.59 (0.11, 3.21) | .26 | 0.89 (0.16, 4.89) |
| 5-6 | 0.32 (0.05, 1.87) | .42 | .42 (0.07, 2.45) | .89 | 0.44 (0.08, 2.60) |
| 6-7 | 0.16 (0.03, 0.93) | .30 | 0.24 (0.04, 1.40) | .95 | 0.39 (0.07, 2.24) |
| 7-8 | 0.16 (0.03, 0.79) | < .01 | 0.38 (0.08, 1.91) | .44 | 0.27 (0.06, 1.36) |
| 8-9 | 0.10 (0.02, 0.39) | < .01 | 0.28 (0.07, 1.10) | .48 | 0.29 (0.07, 1.14) |
| 9-10 | 0.16 (0.03, 0.82) | .83 | 0.14 (0.03, 0.74) | — | — |
| 4-10 | 2.61 (0.87, 7.84) | .37 | 3.16 (1.05, 9.50) | — | — |
a Compares successful TOLAC to uterine rupture;
The time required to progress 1 cm of dilation is similar between the uterine rupture group and both reference groups until 7 cm of dilation is reached. At 7-cm dilation, subjects who experienced uterine rupture spent significantly longer progressing 1 cm in dilation compared to the successful TOLAC group (median time from 7-8 cm: 0.38 vs 0.16 hours, P < .01; median time from 8-9 cm: 0.28 vs 0.1 hours, P < .01). The difference in the median time to progress each centimeter of dilation is approximately 10-15 minutes. More noticeable is the difference in the 95th percentile of time to progress each 1 cm after 7 cm. In women who experienced uterine rupture, the 95th percentile for time required to progress 1 cm after 7 cm was >1 hour, whereas the 95th percentile of time to progress for the successful TOLAC group was <1 hour. The difference in time to progress from 9-10 cm was not significantly different between cases and controls; however, as only 29 cases reached 10 cm, we had limited power to detect a difference between these 2 groups. A partogram was created for cases and the successful TOLAC reference group showing the time to dilate 1 cm from admission ( Figure ).
Because parity has such a strong influence on the time spent in labor, we repeated the analysis excluding all women with a prior vaginal delivery ( Table 4 ). Again, the time required to progress 1 cm in dilation was similar between cases and successful TOLAC controls until 7 cm, at which point cases (n = 98) required longer times to progress in labor compared to controls (n = 226). Women with a failed TOLAC (n = 76) had a similar labor pattern to women with a uterine rupture throughout the course of labor. We were unable to perform the analysis in women with a prior vaginal delivery due to the small number of cases.
| Cervical dilation, cm | Successful TOLAC (n = 226) | P value a | Uterine rupture (n = 98) | P value b | Failed TOLAC (n = 76) |
|---|---|---|---|---|---|
| 3-4 | 0.60 (0.11, 3.43) | .39 | 0.41 (0.07, 2.34) | .49 | 0.61 (0.11, 3.43) |
| 4-5 | 0.47 (0.08, 2.69) | .45 | 0.60 (0.10, 3.47) | .52 | 0.79 (0.14, 4.55) |
| 5-6 | 0.32 (0.05, 1.90) | .39 | 0.43 (0.07, 2.56) | .88 | 0.40 (0.07, 2.37) |
| 6-7 | 0.17 (0.03, 1.01) | .57 | 0.23 (0.04, 1.32) | .44 | 0.12 (0.02, 0.67) |
| 7-8 | 0.17 (0.03, 0.84) | .02 | 0.39 (0.08, 1.94) | .15 | 0.10 (0.02, 0.51) |
| 8-9 | 0.08 (0.03, 0.21) | .03 | 0.38 (0.14, 1.02) | .88 | 0.11 (0.04, 0.30) |
| 9-10 | 0.16 (0.03, 0.82) | .82 | 0.14 (0.03, 0.73) | — | — |
| 4-10 | 2.66 (0.95, 7.41) | .43 | 3.16 (1.13, 8.82) | — | — |
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