During the follicular phase, rising estrogen primarily causes endometrial proliferation.

• A. True
• B. False
• C. Not related
• D. It suppresses estrogen production

Answer: (A)

Rising estrogen during the follicular phase drives the endometrium to proliferate. As the follicles grow, granulosa cells produce more estrogen, which stimulates mitotic activity in the endometrial lining, leading to thickening and the development of glands and blood vessels in preparation for possible implantation. Progesterone is still low before ovulation, so the endometrium remains in the proliferative, not secretory, phase. After ovulation, progesterone from the corpus luteum takes over and promotes secretory changes. So the statement is true because estrogen is the main driver of endometrial proliferation during the follicular phase.