Association of Cervical Effacement With the Rate of Cervical Change in Labor Among Nulliparous Women.

Objective: To assess the association of cervical effacement with the rate of intrapartum cervical change among nulliparous women.

Methods: We conducted a secondary analysis of a prospective trial of intrapartum fetal pulse oximetry. For women who had vaginal deliveries, interval-censored regression was used to estimate the time to dilate at 1-cm intervals. For each given centimeter of progressive cervical dilation, women were divided into those who had achieved 100% cervical effacement and those who had not. The analysis was performed separately for women in spontaneous labor and those who were given oxytocin.

Results: A total of 3,902 women were included in this analysis, 1,466 (38%) who underwent labor induction, 1,948 (50%) who underwent labor augmentation (combined for the analysis), and 488 (13%) who labored spontaneously. For women in spontaneous labor, the time to dilate 1 cm was shorter for those who were 100% effaced starting at 4 cm of cervical dilation (P=.01 to <.001). For women who received oxytocin, the time to dilate 1 cm was shorter for those who were 100% effaced throughout labor (P<.001).

Conclusion: The rate of cervical dilation among nulliparous women is associated with not only the degree of cervical dilation, but also with cervical effacement.

Clinical Trial Registration: ClinicalTrials.gov, www.clinicaltrials.gov, NCT00098709.