During which stage of labor does the baby enter the birth canal?

The correct answer is that the baby enters the birth canal during the second stage of labor. This stage is defined by the time from full cervical dilation (around 10 centimeters) until the delivery of the baby. During this stage, the mother's body experiences strong contractions that help push the baby down through the birth canal. This is the critical moment when the baby's head descends into the canal, followed by the rest of the body.

In contrast, the first stage of labor primarily involves the process of the cervix gradually dilating and effacing in preparation for delivery, but the baby does not enter the birth canal until the second stage begins. The transition stage is part of the first stage and serves as the phase where the cervix finishes dilating, but again, the baby still has not begun its descent. Pre-labor is the phase leading up to active labor and does not involve any significant changes regarding the baby's position in the birth canal.