Final answer:
The third stage of labor starts after the baby is born and involves the expulsion of the afterbirth. This stage can last a short while, and contractions continue to help deliver the placenta.
Step-by-step explanation:
The third stage of labor begins after the birth of the baby, and it is characterized by the delivery of the afterbirth (placenta). This stage may last from a few minutes to a half hour, during which the placenta becomes detached from the uterine wall and is then expelled. A clear sign that this stage has commenced is no longer the contraction of the uterus for birthing purposes but rather contractions that help to expel the placenta. If labor stops before this stage, synthetic oxytocin, known as Pitocin, might be used to restart and maintain labor.