Normal first stage of labor in women undergoing trial of labor after cesarean delivery

OBJECTIVE: To compare first-stage labor patterns in women undergoing trial of labor after cesarean delivery (TOLAC) and those without a previous cesarean to explore whether a uterine scar alters this stage of labor. METHODS: A retrospective cohort study was conducted of consecutive term vertex singletons who reached the second stage of labor. Cervical examinations and obstetric outcomes were collected from medical records. Labor curves of those laboring spontaneously, stratified by TOLAC status, were constructed using a repeated-measures analysis. Interval-censored regression was used to estimate duration of labor, centimeter by centimeter, stratified by TOLAC status and adjusted for race, obesity, macrosomia, and previous vaginal delivery. RESULTS: Of 5,388 consecutive term births, 2,021 labored spontaneously and were included. The 1,881 laboring women with no previous cesarean delivery were compared with 140 women undergoing TOLAC. There was no significant difference in rates of cervical dilation between the groups. The median time for dilation from 4 to 10 cm was 3.0 hours for TOLAC and 2.8 hours for non-TOLAC (P=.52). A post hoc sample size calculation (alpha=0.05) shows 90% power to detect a median difference of 0.4 hours with the fixed sample size available. CONCLUSION: There was no significant difference in first-stage labor curves or cervical dilation rate between women undergoing TOLAC and those without a previous cesarean. Diagnoses of labor disorders should be made with similar standards between those with and without a uterine scar. LEVEL OF EVIDENCE: II.