Association of montevideo units with uterine rupture in women undergoing a trial of labor

OBJECTIVE: To determine if an association exists between Montevideo units (MVUs) and uterine rupture in women undergoing trial of labor after cesarean (TOLAC). STUDY DESIGN: A casecontrol study of women who underwent a TOLAC, comparing uterine rupture (n= 9) to successful vaginal birth after cesarean (VBAC) (n= 48) and failed TOLAC (n=35). MVUs were calculated in 12 10-minute intervals prior to uterine rupture, cesarean delivery, or complete dilation in the VBAC group. MVUs were compared between groups by Wilcoxon rank sum test. The pattern of change of MVUs over time was examined by linear regression mixed models. RESULTS: The MVUs were similar among all groups (medians ranged from 140–175 [VBAC], 145–190 [TOLAC], and 130–195 [ruptures]). The analysis of pattern of change in MVUs over time demonstrated no difference within the VBAC group (p=0.22) or the failed TOLAC group (p = 0.87), or between groups (VBAC and rupture [p=0.56], failed TOLAC and rupture [p = 0.37]). A post-hoc power analysis showed a mean difference of 50 MVUs (SD 45) between VBAC and rupture and 55 MVUs (SD 45) between failed TOLAC and rupture can be detected with a power of 80% at a significance of 0.05. CONCLUSION: There is no association between MVUs and uterine rupture in women undergoing a TOLAC.