(Science: obstetrics) The act of giving Birth to a baby. There are four stages:
The first stage lasts from the onset of labour until there is full dilation (10 cm.) of the cervical os (opening). The first stage of labour is also called the stage of dilatation.
The second stage lasts from the full dilatation of the cervix until the baby is completely out of the birth canal and has been born. The second stage of labour is also called the stage of expulsion.
The third stage lasts from birth of the foetus through expulsion or extraction of the placenta and membranes (afterbirth). The third stage of labour is also called the placental stage.
The fourth stage is the hour or two after delivery when the tone of the uterus is established and the uterus contracts down again.