If a patient had a luteal phase defect, which hormone would most likely be deficient?

If a patient had a luteal phase defect, which hormone would most likely be deficient?

• A. Progesterone
• B. Estrogen
• C. hCG
• D. FSH

Answer: (A)

The key idea is that the luteal phase relies on progesterone from the corpus luteum to prepare and maintain the endometrium after ovulation. Progesterone switches the endometrium from a proliferative state to a secretory one, promoting glandular secretions and blood vessel development so the lining is receptive to an implanting embryo. If there’s a luteal phase defect, progesterone production is insufficient, so the endometrium doesn’t reach the secretory state needed for implantation, leading to infertility or early pregnancy loss. Estrogen helps build the proliferative lining earlier in the cycle but isn’t the main driver of the luteal-phase secretory transformation. FSH starts follicle growth in the follicular phase, not the luteal phase, and hCG supports the corpus luteum only after implantation in pregnancy. So a deficiency in the hormone responsible for sustaining the luteal phase—progesterone—is the most likely cause of a luteal phase defect.

The key idea is that the luteal phase relies on progesterone from the corpus luteum to prepare and maintain the endometrium after ovulation. Progesterone switches the endometrium from a proliferative state to a secretory one, promoting glandular secretions and blood vessel development so the lining is receptive to an implanting embryo. If there’s a luteal phase defect, progesterone production is insufficient, so the endometrium doesn’t reach the secretory state needed for implantation, leading to infertility or early pregnancy loss.

Estrogen helps build the proliferative lining earlier in the cycle but isn’t the main driver of the luteal-phase secretory transformation. FSH starts follicle growth in the follicular phase, not the luteal phase, and hCG supports the corpus luteum only after implantation in pregnancy. So a deficiency in the hormone responsible for sustaining the luteal phase—progesterone—is the most likely cause of a luteal phase defect.