Final answer:
The placenta is typically expelled after delivery during the afterbirth stage, which may last from a few minutes up to 30 minutes. If not spontaneously delivered within approximately 30 minutes, the placenta is considered retained.
Step-by-step explanation:
The process of expelling the placenta after childbirth is known as the afterbirth stage, which is the final phase of labor. Typically, this stage may last from a few minutes to a half hour. The placenta's delivery is crucial to conclude the birthing process and marks the beginning of the postpartum period, which is the time when the mother's body returns to a non-pregnant state over approximately six weeks. If the placenta is not delivered spontaneously within roughly 30 minutes, it is considered to be retained, and further medical intervention may be required.