The luteal phase occurs after ovulation and prepares the uterus for potential implantation. Which hormone is primarily involved in this preparation?

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

Answer: (B)

During the luteal phase, the corpus luteum releases mainly progesterone. This hormone signals the endometrium to switch to a secretory state: the glands secrete nutrients, the stroma becomes more vascular and edematous, and overall the lining becomes receptive to an implanting embryo. Progesterone also helps maintain the uterine lining and dampens contractions to support early pregnancy. While estrogen helps build the lining earlier in the cycle, its role during the luteal phase is secondary to progesterone. LH is important for triggering ovulation and supporting the corpus luteum early on, but the hormone most responsible for preparing the uterus after ovulation is progesterone. If pregnancy doesn’t occur, the corpus luteum regresses and progesterone falls, leading to menses.