What to Know About a Menstrual Cycle

There are 3 phases in the menstrual cycle: follicular, ovulatory, and luteal. (You may hear the period referred to as its own phase, but during your period the body is actually ramping up for ovulation.)

In a typical 28-day cycle, the follicular phase is day 1 to 14, and during this time estrogen is the predominant hormone. Day 1 is the first day you begin to bleed. This is because estrogen and progesterone drop, which triggers the lining of the uterus (the endometrium) to shed, resulting in what is commonly known as a “period” (roughly day 1 through 7). The drop in these hormones also sets off a cascade in the brain. When estrogen and progesterone decrease, the pituitary gland releases follicle-stimulating hormone (FSH), which stimulates the growth of the follicles in the ovaries to ready an egg for ovulation.

Day 12 through 14 is when the ovaries ramp up estrogen production, and this stimulates the pituitary to release luteinizing hormone (LH). The LH surge triggers ovulation and an egg is released. The egg then travels down the fallopian tube and either implants in the endometrium (if fertilized by sperm) or slowly dissolves and passes out of the body (along with the uterine lining) during a period.

Day 15 through 28 of the reproductive cycle is the luteal phase, during which progesterone is the more prominent hormone. Progesterone peaks 5 to 7 days after ovulation. After 28 days if the egg was not fertilized, the reproductive cycle begins again, marking day 1 of a new cycle.