DALLAS – Slow progression of labor beyond 7 cm of dilation in women attempting a trial of labor after cesarean section may signal risk for uterine rupture, findings from a case-control study suggest.
In 99 women who experienced uterine rupture while attempting a trial of labor after cesarean section (TOLAC) and 309 controls who did not experience uterine rupture during TOLAC, the time to progress 1 cm of dilation – after adjustment for prior vaginal delivery – was similar until 7 cm of dilation. Once the women reached 7 cm of dilation, however, a 1 cm progression took significantly longer in those who experienced rupture.
For example, progression from 7 cm to 8 cm took a median of 0.33 vs. 0.15 hours in the uterine rupture patients and the controls, respectively, and the progression from 8 cm to 9 cm took a median of 0.24 vs. 0.1 hours in the groups, respectively, Dr. Lorie Harper of Washington University in St. Louis reported at the annual meeting of the Society for Maternal-Fetal Medicine.
"This works out to approx 10-13 minutes longer for the median time to progress 1 cm in the uterine rupture group," she said, noting that the differences were particularly striking at the 95th percentile of time per 1 cm of dilation; for women with a successful trial of labor, each 1 cm of dilation after 7 cm took less than 1 hour, while at the 95th percentile, progression of each 1 cm of dilation after 7 cm took at least 1 hour.
The findings are from a secondary analysis of data from a nested case-control study of women attempting TOLAC within a 17-center retrospective cohort study of women with a prior low transverse cesarean section. Cases included women who experienced uterine rupture, and controls included women attempting TOLAC who reached 10 cm dilation. An additional reference group included 110 women with a failed TOLAC who ultimately underwent repeat cesarean section, and no significant difference was seen between this group and the cases in terms of time to progress after 7 cm. All subjects had only one prior cesarean section.
Uterine rupture for this study was explicitly defined, a priori, as a full-thickness disruption of the uterine wall accompanied by clinical signs, Dr. Harper said.
The cases and controls from both reference groups were similar with respect to age, gravidity, diabetes, hypertension, and type of hospital, although the rate of prior vaginal delivery and black race both were more common in the reference groups. The three groups also were comparable with respect to intrapartum characteristics such as epidural use and gestational age at delivery, although those who experienced uterine rupture were more likely to have been induced and to have received Pitocin, she noted.
Although the case-control design of this study has inherent limitations such as possible selection bias, the study also has strengths, including the large study population of nearly 14,000 women in the original retrospective cohort, she said.
The findings suggest that a protracted labor prior to 7 cm of dilation does not necessarily signify uterine rupture in women attempting a TOLAC, as it was not uncommon during this period for the women to require 2 hours to progress 1 cm, and some still reached 10 cm, Dr. Harper said.
After 7 cm, however, labor dystocia should raise suspicion for uterine rupture in this population, she said.
Although the findings don’t necessarily suggest that intervention such as cesarean delivery is indicated in those with slow progression after 7 cm, they do underscore the need for more careful and frequent monitoring for signs of uterine rupture during active labor in women attempting a TOLAC.
"Instead of waiting 2 hours to check them, maybe they should be checked in an hour to make sure they’re progressing," she said.
This study was supported by the Eunice Kennedy Shriver National Institute of Child Health and Human Development. Dr. Harper said she had no relevant financial disclosures.