Labour can be clearly divided into three phases (a bit like trimesters of pregnancy). The first starts with your regularly experiencing uterine contractions which are causing your cervix to open. The end of the first stage also marks the start of the second. The full dilatation of your cervix, is the beginning of the second stage and ends with the delivery of the baby. The third starts at the birth of the baby and ends with the deilvery of the placenta.