• first stage of labor;
  • labor onset;
  • obstetric labor;
  • parturition;
  • pregnancy

Introduction: Laboring women are often admitted to labor units under criteria that are commonly associated with the onset of active-phase labor (i.e., cervical dilatation of 3–5 cm in the presence of regular contractions). Beginning with these criteria through complete dilatation, this systematic review describes labor duration and cervical dilation rates among low-risk, nulliparous women with spontaneous labor onset.

Methods: Studies published in English (between 1990 and 2008) were identified via MEDLINE and CINAHL searches. Data were abstracted and weighted “active labor” durations (i.e., from 3–5 cm through complete dilatation) and linear dilation rates were calculated.

Results: Eighteen studies (n = 7009) reported mean “active labor” duration. The weighted mean duration was 6.0 hours, and the calculated dilation rate was 1.2 cm per hour. These findings closely parallel those found at the median. At the statistical limits, the weighted “active labor” duration was 13.4 hours (mean + 2 standard deviations) and the dilation rate was 0.6 cm per hour (mean − 2 standard deviations).

Discussion: These findings indicate that nulliparous women with spontaneous labor onset have longer “active” labors and therefore slower dilation rates than are traditionally associated with active labor when commonly used criteria are applied as the starting point. Revision of existing active labor expectations and/or criteria used to prospectively identify active phase onset is warranted.