Latent phase The latent phase of labor, also called prodromal labor, may last many days and the contractions are an intensification of the Braxton Hicks contractions that may start around 26 weeksgestation. Cervical effacement occurs during the closing weeks of pregnancy and is usually complete or near complete, by the end of the latent phase. Cervical effacement or cervical dilation is the thinning and stretching of the cervix. The degree of cervical effacement may be felt during a vaginal examination. A 'long' cervix implies that not much has been taken into the lower segment, and vice versa for a 'short' cervix. Latent phase ends with the onset of active first stage; when the cervix is about 3 cm dilated. prodromal laborcontractionsBraxton Hicks contractionsgestationCervical effacementpregnancycervical dilationcervixprodromal laborcontractionsBraxton Hicks contractionsgestationCervical effacementpregnancycervical dilationcervix

First stage: dilation There are several factors that midwives and clinicians use to assess the laboring mother's progress, and these are defined by the Bishop Score. The Bishop score is also used as a means to predict whether the mother is likely to spontaneously progress into second stage (delivery). Bishop ScoreBishop Score The first stage of labor starts classically when the effaced (thinned) cervix is 3 cm dilated. There is a variation in this point as some women may have active contractions prior to reaching this point, or they may reach this point without regular contractions. The onset of actual labor is defined when the cervix begins to progressively dilate. Rupture of the membranes, or a blood stained 'show' may or may not occur at or around this stage. contractions

Uterine muscles form opposing spirals from the top of the upper segment of the uterus to its junction with the lower segment. During effacement, the cervix becomes incorporated into the lower segment of the uterus. During a contraction, these muscles contract causing shortening of the upper segment and drawing upwards of the lower segment, in a gradual expulsive motion. This draws the cervix up over the baby's head. Full dilation is reached when the cervix has widened enough to allow passage of the baby's head, around 10 cm dilation for a term baby. cervix

The duration of labour varies widely, but active phase averages some 8 hours for women giving birth to their first child ("primiparae") and 4 hours for women who have already given birth ("multiparae"). Active phase arrest is defined as in a primigravid woman as the failure of the cervix to dilate at a rate of 1.2 cm/hr over a period of at least two hours. This definition is based on Friedman's Curve, which plots an ideal rate of cervical dilation and fetal descent during active labor. Some practitioners may diagnose "Failure to Progress", and consequently, perform a Cesarean. The duration of labour varies widely, but active phase averages some 8 hours for women giving birth to their first child ("primiparae") and 4 hours for women who have already given birth ("multiparae"). Active phase arrest is defined as in a primigravid woman as the failure of the cervix to dilate at a rate of 1.2 cm/hr over a period of at least two hours. This definition is based on Friedman's Curve, which plots an ideal rate of cervical dilation and fetal descent during active labor. Some practitioners may diagnose "Failure to Progress", and consequently, perform a Cesarean.

No effaced no dilation

Fully effaced 1 cm dilation

5 cm dilation

Fully dilated at 10 cm