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More than just periods: Menstrual cycle 101 

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The better you understand your unique menstrual cycle, the better you can understand your overall health.

Although the average menstrual cycle is 28 days, a cycle can actually be a few days longer or shorter and still be considered normal. Cycle length can also vary a little from cycle to cycle and still be considered normal.

Hormonal changes in the body trigger each cycle phase: menstrual, proliferative, ovulatory, and luteal. And while your period is the most recognizable phase, the other three are equally important and impact your energy levels, immune system, moods, and sleep patterns differently. Let’s dive in.

What are the menstrual cycle phases?

The body performs different functions throughout the four phases of the menstrual cycle, each of which plays a unique role in the reproductive process:

Proliferative: During the proliferative phase, ovarian follicles (structures in the ovary that each contain a single egg) mature and prime themselves for ovulation. Your hormones perform different functions that are geared toward the goal of producing an egg for fertilization during ovulation, the next phase. Although many follicles start maturing during the proliferative phase, usually only one eventually proves dominant, and becomes the sole egg available during ovulation.

Ovulatory: The ovulatory phase begins as a hormone surge forces the dominant egg to break free from its follicle and nest in a fallopian tube, where it will disintegrate if not fertilized within about 24-36 hours. Ovulation is the only phase in which you can get pregnant. But because sperm can live for up to five days in the reproductive system, if sperm is present in the short time leading up to ovulation, this can also result in conception.

Luteal: Following ovulation, the follicle that released the egg transforms into a corpus luteum, a structure that produces the pregnancy hormone progesterone. Progesterone thickens the lining of the uterus in preparation for a fertilized egg to make its home there for the next nine months. If conception occurs, the corpus luteum continues to produce progesterone to maintain a healthy pregnancy. If the egg is not fertilized, the corpus luteum ceases its progesterone production after about two weeks. This drop in progesterone signals menstruation to begin.

Menstruation: The onset of menstruation is considered to be the start and end of a menstrual cycle, as it signifies the end of an opportunity for fertilization for one egg (and the beginning for millions more). Menstruation is triggered when the corpus luteum of the last cycle’s unfertilized egg ceases to produce progesterone, usually occurring about two weeks after ovulation, causing the uterine lining to shed, along with a bit of blood. The length and intensity of a period varies from person to person and cycle to cycle, but usually lasts between 4-6 days. Once the period stops, the proliferative phase begins again, starting the reproductive process anew.

Reviewed by the Ovia Health Clinical Team

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  • Mayo Clinic Staff. “Menstrual cycle: What’s normal, what’s not.” Mayo Clinic. Mayo Clinic, 4/16/2013. Web.
  • “Patient Fact Sheet: Am I Ovulating?” ASRM. American Society for Reproductive Medicine, 2014. Web.

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