Which hormone produced by the ovary has the highest concentration during the luteal phase of the ovarian cycle?

During the luteal phase of the ovarian cycle, the main hormone produced by the corpus luteum is progesterone. After ovulation, the ruptured follicle transforms into the corpus luteum, which secretes progesterone in significant amounts. This hormone plays a crucial role during the luteal phase by preparing the endometrium for potential implantation of an embryo, aiding in the maintenance of early pregnancy if fertilization occurs.

Progesterone's primary function is to alter the uterine lining, making it more suitable for a fertilized egg to implant and grow. Its levels peak during this phase, ensuring that the uterine environment is optimal for supporting a developing embryo. While estradiol (a form of estrogen) is also produced during this stage, its concentration is markedly lower compared to progesterone. Follistatin is not significantly involved in the luteal phase, and while it is related to follicle development, it does not play a primary role in this specific phase. Thus, progesterone's predominant role and highest concentration during the luteal phase make it the correct answer.