After the corpus luteum degenerates, progesterone levels fall significantly. The corpus luteum forms from the remains of the ovarian follicle after ovulation and is responsible for producing progesterone during the luteal phase of the menstrual cycle. This hormone plays a crucial role in maintaining the uterine lining for possible implantation of a fertilized egg.
When the corpus luteum eventually degenerates if pregnancy does not occur, its production of progesterone ceases. As a result, progesterone levels drop, leading to the breakdown of the uterine lining and the start of menstruation. This decrease in progesterone is a vital signal in the menstrual cycle as it leads the body to prepare for a new cycle.
The other options do not accurately reflect the physiological process that occurs after the degeneration of the corpus luteum, making the correct answer clearly associated with this critical hormonal change.