The menstrual cycle consists of four main phases, each characterized by specific hormonal and physiological changes:
- Menstrual Phase (Menstruation)
This phase begins on the first day of bleeding and typically lasts 3 to 7 days. The uterine lining (endometrium) sheds if no pregnancy has occurred, resulting in menstrual bleeding composed of blood, mucus, and tissue from the uterus
- Follicular Phase
Starting on the first day of menstruation and lasting about 13 to 14 days, this phase involves the thickening of the uterine lining and the growth of ovarian follicles stimulated by follicle-stimulating hormone (FSH). Usually, one follicle matures into an egg. Estrogen levels rise during this phase, leading to the regeneration of the endometrium
- Ovulation
Occurring roughly mid-cycle (around day 14 in a 28-day cycle), ovulation is the release of a mature egg from the dominant follicle in the ovary. This phase is triggered by a surge in luteinizing hormone (LH) and represents the period of highest fertility
- Luteal Phase
Following ovulation, the ruptured follicle transforms into the corpus luteum, which secretes progesterone. This hormone prepares the endometrium for potential implantation by thickening it and making it more receptive. If fertilization does not occur, progesterone levels fall, leading to the breakdown of the uterine lining and the start of menstruation, thus beginning a new cycle. The luteal phase typically lasts about 14 days
These phases collectively prepare the body for pregnancy each month and regulate the menstrual cycle length, which averages around 28 days but can vary between individuals
