During childbirth, what is primarily responsible for the expulsion of the fetus?

The expulsion of the fetus during childbirth is primarily due to myometrial contraction. The myometrium is the muscular layer of the uterus, and its contractions play a crucial role in the labor process. During labor, the muscles of the myometrium contract rhythmically, which helps to push the fetus down the birth canal and out of the uterus.

These contractions increase in intensity and frequency as labor progresses, facilitating the passage of the fetus. The physical force generated by these contractions is essential for effective delivery and ensures that the baby moves through the cervix and into the vaginal canal.

While cervical dilation and other factors contribute to the overall childbirth process, the driving force behind the actual expulsion of the fetus is the powerful and coordinated contractions of the myometrium. It is these contractions that ultimately lead to the delivery of the baby, making them the primary mechanism responsible for this critical stage of human reproduction.