Which hormone promotes uterine contractions during labor and helps control postpartum bleeding?

• A. Estrogen
• B. Prolactin
• C. Oxytocin
• D. Testosterone

Answer: (C)

Oxytocin is the hormone that directly drives uterine contractions during labor and, by promoting strong, coordinated contractions after delivery, helps compress uterine blood vessels to limit bleeding (postpartum hemorrhage). It is released from the posterior pituitary in response to cervical dilation and stimulation, and its action on uterine smooth muscle is what moves labor along and helps achieve hemostasis after the placenta is delivered.

Estrogen, while important in preparing the uterus for labor by increasing the density of oxytocin receptors and enhancing contractile readiness, does not by itself trigger contractions. Prolactin mainly governs milk production, not uterine contractions or postpartum bleeding. Testosterone is not part of the typical hormonal regulation of labor or postpartum uterine hemostasis.