OBJECTIVE: Studies using contemporary populations and modern statistical methods have redefined our understanding of cervical dilation in labor. However, modern norms for fetal descent in labor have not been developed. We sought to estimate norms for fetal descent and estimate the expected fetal station for given cervical dilations.
METHODS: A retrospective cohort study of consecutive-term, vertex singletons who delivered vaginally. Detailed history, labor, and delivery information, including cervical examinations, were collected. A repeated-measures analysis was used to construct average descent curves. Interval-censored regression was used to estimate duration of labor between levels of station and to estimate the median station at a given dilation. Each analysis was stratified by parity and labor type (spontaneous compared with induced or augmented).
RESULTS: Of 4,618 consecutive-term spontaneous vaginal deliveries, 1,526 (33%) were nulliparous. Sixty-one percent were augmented or induced. Multiparous women had faster fetal descent at all stations except from +2 to +3 station. The median time to descend from one station point to another ranged from 0.1 to 1.6 hours, but the 95th percentiles encompassed over 12 hours at the same high-station among nulliparous women who achieved vaginal delivery. Fetal descent was more rapid in women who labored spontaneously without augmentation. Multiparous women tended to have a higher station than nulliparous women until late in the first stage.
CONCLUSION: Multiparous women and women who are not augmented or induced have faster fetal descent. There is wide variation in the expected station by increments of dilation. However, 95% of women have a fetal station of 0 or lower at complete cervical dilation.
LEVEL OF EVIDENCE: II