What Are the Phases of the Menstrual Cycle?

If you're a woman, you may know that your menstrual cycle is caused by changes in hormone levels. The changes signal your body to prepare for a fertilized egg to be implanted, causing pregnancy. You might have wondered, however, what stages your body goes through during the entire menstrual cycle. Menstruation has two cycles and four phases. Some of the phases occur within the same cycle.

The Two Cycles

• The two cycles are the ovarian cycle and the uterine cycle. The follicular phase, ovulation and the luteal phase occur during the ovarian cycle. The proliferative phase and the secretory phase occur during the uterine cycle.

The Follicular Phase

• The first day of your period begins the follicular phase, and it lasts until ovulation. It is called the follicular phase, because the egg is growing and maturing inside a small sac known as the follicle.

Ovulation

• Ovulation is next, coming around the 14th day of the complete menstrual cycle. Ovulation occurs when the level of the luteinizing hormone, sometimes called LH, surges, and this surge happens just before the ovary releases the egg.

The Luteal Phase

• Once the egg is released from the ovary, causing ovulation, you enter the luteal phase. This phase lasts until the first day you start your period. This phase takes its name from the corpus luteum, which means yellow body in Latin. This is a structure that grows in the spot in the ovary from which the mature egg was released when ovulation occurred. Although it is a separate cycle, the uterine cycle is occurring at the same time as the ovarian cycle, and has its own two phases.

Proliferative Phase

• After your period ends, and until you ovulate again, you are going through the proliferative phase. During this time, the lining of your uterus is growing and thickening again, preparing for a fertilized egg to become implanted, which in turn will cause pregnancy.

Secretory Phase

• Once ovulation has occurred again, and lasting until you start your period, the glands in the lining of your uterus begin secreting proteins. This, too, is in preparation for implantation of a fertilized egg.

  If, however, the egg does not implant, the uterine lining, also known as the endometrium, starts breaking down, and the glands no longer secrete proteins. The lining sloughs off of the uterine walls and is passed out of your body, and this is called menstruation.

  Menstruation usually lasts between three to five days; however, your period may be longer or it may be shorter.