What are the main phases of the menstrual cycle?

The menstrual cycle is a recurring process involving hormonal fluctuations that prepare the body for pregnancy. While it is customary to count the first day of menstruation as the start of the cycle, the process is typically divided into two primary phases separated by ovulation.12

The Two Primary Phases

• Follicular Phase: Lasting approximately 14 days, this phase begins with the maturation of ovarian follicles under the influence of follicle-stimulating hormone. During this time, the endometrium (uterine lining) thickens and proliferates in response to rising estrogen levels.123
• Luteal Phase: Following ovulation, the ruptured follicle transforms into the corpus luteum. This structure secretes large amounts of progesterone, which prepares the endometrium to receive a fertilized egg. If fertilization does not occur, the corpus luteum degenerates, hormone levels drop, and the uterine lining is shed, marking the onset of the next menstrual period.123

These phases are regulated by a complex feedback loop involving the pituitary gland and the hypothalamus.12