Prostaglandin levels increase late in pregnancy secondary to elevated which hormone?

• A. Relaxin
• B. Progesterone
• C. Estrogen
• D. Oxytocin

Answer: (C)

In late pregnancy, rising estrogen relative to progesterone signals the uterus to prepare for labor. Estrogen increases the production of prostaglandins by upregulating enzymes like COX-2 in uterine tissues and membranes, leading to more PGE2 and PGF2α. These prostaglandins promote cervical ripening and enhance uterine contractions, helping initiate labor. While oxytocin later stimulates contractions and prostaglandin release during labor, the increase in prostaglandins at this stage is driven primarily by elevated estrogen. Progesterone acts to keep the uterus quiet, and relaxin contributes to cervical changes but does not primarily drive prostaglandin rise.