This hormone comes from your baby, placenta and tissues within your uterus and increased levels late in pregnancy change the ratio of estrogen to progesterone.

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

Answer: (B)

Corticotropin-releasing hormone (CRH) is produced by the baby, placenta, and uterine tissues, and its levels rise as term approaches. This late-pregnancy surge triggers fetal cortisol production, which leads to more estrogen being produced relative to progesterone. That shift in the estrogen-to-progesterone ratio makes the uterus more responsive to contractions and promotes labor readiness through mechanisms like increased oxytocin receptor expression and uterine excitability. Other hormones have important roles in labor, but they do not primarily drive this specific shift in the estrogen–progesterone balance.