Labor refers to uterine contractions resulting in progressive dilation and effacement of the cervix, accompanied by descent and expulsion of the fetus. “Abnormal labor,” “dystocia,” and “failure to progress” are traditional but imprecise terms that have been used to describe a labor pattern deviating from that observed in the majority of women who have spontaneous vaginal deliveries. These labor abnormalities are best described as protraction disorders (ie, slower than normal progress) or arrest disorders (ie, complete cessation of progress).
Although determining whether labor is progressing normally is a key component of intrapartum care, determining the onset of labor, measuring its progress, and evaluating the factors (power, passenger, pelvis) that affect its course constitute an inexact science.
Terminology — There are three stages of labor:
●First stage – Time from onset of regular contractions to complete cervical dilation. However, the precise time of onset of regular contractions is very difficult to determine since the normal uterus contracts intermittently and irregularly throughout gestation and the first regular contractions of labor are mild and infrequent.
The first stage consists of a latent phase and an active phase. The latent phase is characterized by gradual cervical change and the active phase is characterized by rapid cervical change (at least 1 cm dilation per hour).
●Second stage – Time from complete cervical dilation to expulsion of the fetus.
Some clinicians divide the second stage of labor into a passive phase (from complete cervical dilation to onset of active maternal expulsive efforts) and an active phase (from beginning of active maternal expulsive efforts to expulsion of the fetus) .