What is the slowest-yet-normal cervical dilation rate among nulliparous women with spontaneous labor onset?

OBJECTIVE: To integrate research literature that has provided insights into the cervical dilation rate that may best describe the slowest-yet-normal dilation rate among nulliparous women when beginning with criteria commonly associated with active labor onset. DATA SOURCES: A literature search from 1950 through 2008 was conducted using the Medline electronic database, reference lists from identified articles, and other key references. STUDY SELECTION: Research reports written in English with a focus on the cervical dilation and/or labor duration of low-risk, nulliparous women with spontaneous labor onset. DATA EXTRACTION: Classic and contemporary research literature was reviewed and organized under the following subheadings: Friedman Studies, Partograph Studies, Active Management of Labor Studies, Additional Studies. DATA SYNTHESIS: An integrative review of the literature approximated the slowest-yet-normal cervical dilation rate for nulliparous women when beginning with criteria commonly associated with active labor.
CONCLUSIONS: The slowest-yet-normal linear dilation rate approximates 0.5 cm/hour for low-risk, nulliparous women with spontaneous labor onset when starting at dilatations traditionally associated with active labor onset. However, this linear rate must be evaluated judiciously in light of the physiological acceleration of dilation that occurs during typical labor. Given this, cervical dilation for this population is likely slower than 0.5 cm/hour in earlier active labor and faster in more advanced active labor. Faster dilation expectations (e.g., 1 cm/hour) likely contribute to an overdiagnosis of dystocia ("slow, abnormal progression of labor") in contemporary practice and, subsequently, to an overuse of interventions aimed at accelerating labor progress.