Abstract
Objective To estimate the natural history of cervical effacement in labor.
Study Design This is a retrospective cohort study of term, vertex, singletons who reached 10 cm
of cervical dilation from 2010 to 2014. Interval-censored regression was used to estimate
the median number of hours between changes in effacement (measured in centimeters
of the residual cervix) and to estimate the median effacement at a given cervical
dilation. Analysis was stratified by parity and labor type.
Results In total, 7,319 patients were included. Multiparas had faster effacement from 1 cm
to complete effacement than nulliparas, but nulliparas were significantly more effaced
at each cervical dilation. Patients in spontaneous labor had faster effacement and
were significantly more effaced at each centimeter of cervical dilation than those
who were induced or augmented. Once active labor was established (>6 cm of cervical
dilation), 95% of patients had an effacement of 1 cm or less. By 8 cm of cervical
dilation, 50% of all patients were completely effaced.
Conclusion There is a wide range in the normal length of time for the progression of cervical
effacement. However, once a patient is in active labor, 95% of patients have effaced
to 1 cm or less.
Keywords
effacement - labor - labor disorders - cervical effacement - first stage of labor
- cervix
