The phases of the cycle
The menstrual cycle is the recurring sequence that prepares the body for a possible pregnancy. It begins with menstruation, the shedding of the uterine lining, during the early follicular phase. During the follicular phase, rising follicle-stimulating hormone helps an ovarian follicle mature while estrogen rises and rebuilds the lining. A surge in luteinising hormone then triggers ovulation, the release of an egg, around the middle of a typical cycle.
Although twenty-eight days is often quoted as average, normal cycle length varies considerably between people and from cycle to cycle.
What the luteal phase does
After ovulation, the structure left behind in the ovary, the corpus luteum, produces progesterone, which stabilises and prepares the uterine lining for a fertilised egg. If pregnancy does not occur, the corpus luteum breaks down, progesterone and estrogen fall, and the lining is shed, starting the next cycle.
Cycle patterns are influenced by age, stress, weight, and many other factors. This is general educational information about reproductive physiology, not medical advice; concerns about cycle changes should be discussed with a qualified clinician.