Labour has started when contractions come regularly every 4 to 5 minutes and last at least a minute. In 10 to 15 per cent of cases labour starts with the waters breaking.
Contractions open the cervix; this is called dilation. With a first baby dilation takes 12 to 20 hours on average. With later babies it is usually quicker. Stress can slow dilation down, so try to relax as well as you can between contractions. A shower or a bath can help.
The midwife checks regularly how far dilation has progressed.
Full dilation
At 10 cm the cervix is completely open: this is full dilation. Usually you feel the urge to push at that point, and this is normally the moment you can start pushing actively. Pushing means bearing down with the rhythm of the contractions to move your baby out. With a first baby pushing can take one to one and a half hours. With later babies this stage too is usually quicker.