Answer: Second stage of labour
Explanation: The second stage of labour begins with exactly what is stated in the question, that is, when the cervix is open, i.e when the baby enters the vaginal opening. From the moment the cervix is opened or, as it is also called, when the cervix is fully dilated, the second phase begins, which lasts until the baby comes out, i.e it ends with the birth of the baby. This phase is followed by strong contractions by which the baby is pushed down the birth canal, that is, pushing the baby towards birth. The second phase, i.e contractions until the baby is born, can last from 20 minutes to several hours. Contractions can often last less than a minute to a minute and a half, between which there is a period of three to five minutes, when the mother is resting from heavy contractions.