A deficiency in estrogen during the follicular phase will result in which outcome?

• A. A failure of embryo implantation.
• B. An increased length of the menstrual cycle.
• C. A lack of Graafian follicle release from the ovary.
• D. An incomplete development of the endometrium.

Answer: (D)

Estrogen in the follicular phase drives the thickening and proliferation of the endometrium to prepare for a possible pregnancy. When estrogen is deficient, this proliferative drive is blunted, so the endometrium doesn’t develop adequately and remains underprepared. That direct result—incomplete development of the endometrium—best explains the outcome. Implantation problems are a consequence of a poorly prepared lining, but the immediate effect of low estrogen during the follicular phase is the insufficient endometrial proliferation. The other options involve later or indirect effects (such as ovulation triggering or cycle length) that are not the primary direct outcome of estrogen deficiency in this phase.