Normal Labour

Abstract

Labour is diagnosed when regular painful uterine contractions effect progressive cervical dilatation. Passage of blood-stained mucus (the show) usually occurs early in labour and the membranes rupture late in the first stage. The rate of cervical dilatation is plotted as a sigmoid curve with a latent phase from 0 to 3 cm, followed by an active phase until delivery. In primiparae the cervix dilates at 1–2 cm/h between 1 and 5 cm and 2–3 cm/h between 5 and 10 cm. Progress is judged by dilatation of the cervix and descent of the presenting part (station), i.e. its relationship to the ischial spines, and not on the frequency (normally once every 2–3 min), duration (normally 30–60 s) or intensity of the contractions or whether the membranes have ruptured. Normal labour involves the coordinated action of powers (uterine contractions), passage (bony and soft) and passenger (size, presentation and position of fetus(es)).