Which hormone stops ovulation during pregnancy?

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

Answer: (D)

Progesterone is the hormone that stops ovulation during pregnancy because it creates a strong negative feedback on the hypothalamus and pituitary, keeping GnRH, LH, and FSH levels low. With low gonadotropins, no new follicle matures and no ovulation occurs. Early in pregnancy the corpus luteum provides the progesterone, and later the placenta can take over production to maintain its high levels. This progesterone-dominated environment also supports the uterine lining and reduces uterine contractions, helping maintain pregnancy. Estrogen helps build the uterine lining and has its own regulatory roles, but it isn’t the primary signal that prevents ovulation during pregnancy. Testosterone isn’t the regulator of ovulation in females, and prolactin mainly drives milk production (and has secondary effects on GnRH), not the direct suppression of ovulation like progesterone does.