Afterbirth pains are primarily caused by which of the following?

The primary cause of afterbirth pains, also known as postpartum uterine contractions, is the contraction of the uterus. Following delivery, the uterus undergoes a series of contractions to return to its pre-pregnancy size and to help control bleeding by compressing the blood vessels within the uterine wall. These contractions can feel similar to menstrual cramps and are more pronounced during subsequent pregnancies due to the increased muscle tone and memory of the uterus, leading to stronger and more noticeable afterpains.

Understanding this physiological process is important for midwifery practice, as afterbirth pains can significantly affect a postpartum individual's comfort and recovery. Monitoring the intensity of afterbirth pains can be an indicator of uterine involution and overall postpartum health, guiding appropriate interventions if needed. While the other options may relate to postpartum physiology, they do not specifically cause afterbirth pains in the way uterine contractions do.