How do bearing-down efforts help during the second stage of 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 the second stage of labor, also known as the stage of expulsion, voluntary bearing-down efforts significantly assist the delivery process. When the mother takes a deep breath and contracts her abdominal muscles, she creates increased intra-abdominal pressure that can equal or even exceed the force of involuntary uterine contractions.1

These efforts are highly effective, potentially doubling the total force applied to the fetus. This combined pressure—derived from both the uterus and the abdominal muscles—is exerted on the child’s buttocks and transmitted along the vertebral column. This force is essential for driving the child's head into and through the pelvis, facilitating the complex movements of flexion, rotation, and extension required for the child to be born.12