Which hormone is produced by the baby, placenta, and uterine tissues and rises late in pregnancy to shift the estrogen-to-progesterone balance?

• A. Estrogen
• B. Prostaglandins
• C. Relaxin
• D. Corticotropin-releasing hormone (CRH)

Answer: (D)

Late in pregnancy, corticotropin-releasing hormone (CRH) produced by the placenta and fetal tissues rises, shifting the estrogen-to-progesterone balance toward estrogen dominance. This CRH surge stimulates the fetal-adrenal axis, increasing fetal cortisol, which boosts placental estrogen production while progesterone’s quieting influence becomes outweighed. The result is greater uterine excitability, higher prostaglandin production, and cervical ripening— preparing the uterus for labor. Prostaglandins and relaxin also play roles in labor-related changes, but CRH is the key signal that drives the shift in the hormonal balance itself, linking fetal/placental signaling to the onset of labor.