Which hormone is produced by the baby, placenta and tissues within the uterus and increases late in pregnancy to change the estrogen-to-progesterone ratio?

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

Answer: (C)

Corticotropin-releasing hormone (CRH) is the hormone described. CRH is produced by the fetus (its tissues), the placenta, and uterine/fetal membranes, and its levels rise markedly as term approaches. This placental/fetal CRH surge drives increased fetal cortisol, which in turn boosts placental estrogen production. The result is a shift in the balance toward estrogen relative to progesterone. That higher estrogen-to-progesterone ratio promotes uterine readiness for labor by enhancing uterine contractions (in part through more prostaglandin production and strengthened myometrial connections). Prostaglandins themselves rise to support contractions, but they are part of the downstream effects of the CRH-driven shift, not the initiating signal described in the question.