Variability in rate of cervical dilation in nulliparous women at term.

Background: Cervical dilatation is commonly documented on a partogram indicating the expected rate of progress of labor. Although deviations from such a line can be used to indicate abnormal progress, what constitutes the "normal" rate of cervical dilation is still largely unknown. The objectives of this study were to assess the variability of the rate of cervical dilation in nulliparous women and to determine whether the rate of labor was independent of dilation on admission.

Methods: We analyzed a cohort of consecutive nulliparous women with spontaneous labor at term and singleton fetuses in cephalic presentation. Exclusion criteria were gestational age less than 37 weeks, induction of labor, or the presence of a uterine scar. Management of labor was standardized using set protocols of care. Active labor was diagnosed as regular contractions every 10 minutes or less, lasting more than 40 seconds, with cervical effacement more than 80 percent and dilation of 2 cm. Vaginal examinations were performed by a dedicated midwife every 2 hours. Amniotomy was performed for slow progress or arrest of dilation over 2 hours. Oxytocin was administered for arrest of cervical dilation for 2 hours with membranes ruptured. Data pertaining to cases ending in cesarean delivery were included up to the time of cesarean section.

Results: The study sample comprised 1,119 women at 39.7 ± 1.1 weeks with an average duration of labor of 4.1 ± 2.4 hours. The rate of oxytocin use was 27 percent and of epidural analgesia 5 percent. The rate of oxytocin use was inversely related to cervical dilation on admission. Cesarean delivery was performed in 6 percent of women. Duration of labor at each centimeter of cervical dilation on admission showed a broad distribution (e.g., at 4 cm: median = 5.5, range: 0.8-12.5 hr). The rate of labor progression (expressed as the slope of the dilation-vs-time curve) was approximately 1.5 cm/hr, and it was essentially independent of cervical dilation on admission (r = 0.034, p = 0.267). A deceleration phase seemed to be present toward the end of the active phase of labor (approximately 9 cm).

Conclusion: In our setting, the rate of labor in nulliparous women at term was highly variable, and it did not appear to be affected by cervical dilation on admission.