Normally labour and subsequent delivery occurs 38 to 40 weeks after the last menstrual period. If labour occurs before 37 weeks of pregnancy, it is considered premature and after 42 weeks, is termed post mature (postterm) labour. Labour can be divided into three stages: The first stage is from the earliest contractions up to the time of birth. It is generally the longest and hardest and involves the effacement (thinning out) and dilation opening up) of the cervix to 10 centimetres (5 fingerbreadths). Stage one has 3 phases.