What phase of the menstrual cycle is characterized by the highest levels of progesterone?

The luteal phase of the menstrual cycle is characterized by the highest levels of progesterone. After ovulation occurs, the ruptured follicle transforms into a structure known as the corpus luteum, which secretes progesterone. This hormone plays a crucial role in preparing the endometrium (the lining of the uterus) for potential implantation of a fertilized egg. Increased levels of progesterone during the luteal phase help maintain the uterine lining and support early pregnancy if fertilization occurs. If pregnancy does not occur, progesterone levels will drop, leading to the onset of menstruation and the start of a new cycle.

In contrast, the follicular phase is marked by rising estrogen levels, ovulation involves a surge in luteinizing hormone (LH) rather than progesterone, and the menses phase is when hormone levels are quite low as the uterine lining is shed.