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How does oxytocin affect the uterus during labor?

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A series of medical illustrations showing the stages of childbirth: the baby's position at the onset of labor, flexion, internal rotation of the head, extension, external rotation of the head, and the uterus immediately after birth with the placenta and umbilical cord. — birth Sequential changes in the position of the child during labour.

During labor, oxytocin acts as a facilitator by stimulating contractions of the uterus. It achieves this by binding to specific receptors located on the smooth-muscle cells of the uterine wall.1

As pregnancy reaches term, the number of these oxytocin receptors increases significantly, which makes the uterus much more sensitive to the hormone. During the process of fetal expulsion, the posterior pituitary gland releases oxytocin in pulses, though the hormone can also be secreted locally by intrauterine tissues. While oxytocin is not strictly essential for labor to occur—as individuals lacking it can still experience normal parturition—it is frequently used in obstetric practice to induce or strengthen labor when it is flagging or prolonged.12