The Four Phases Explained

During the menstrual cycle, simultaneous changes occur in the

  • uterus: endometrium

  • ovary: ovarian follicle and corpus luteum

  • cervix: changes in cervical fluid and sensation

the menstrual cycle changes in the uterus, ovary, and cervix are depicted in this graph

Menstrual Phase

image of the menstrual phase: the menstrual bleed

  • the uterus is shedding its lining

  • blood is exiting through the vaginal opening to the vulva

  • the cervix is open to let blood flow

  • estrogen and progesterone are low

image of the relative ovarian / menstrual hormones depicted in a graph

Follicular Phase

follicular phase of the menstrual cycle depicted by the changes in the uterus, cervix, and ovary

  • the uterus begins making new lining, entering the early proliferative phase

  • ovarian follicles begin developing in the presence of estrogen

  • cervical fluid production begins developing in the presence of estrogen

  • the fertility window begins

menstrual cycle hormones throughout the phases of the cycle

Ovulatory Phase

ovulatory phase of the menstrual cycle depicted by the changes in the ovary, uterus, and cervix

  • the uterine lining continues to thicken in the late proliferative phase

  • high levels of luteinizing hormone trigger the release of the egg, and ovulation occurs

  • cervical fluid production peaks from the presence of estrogen and LH

  • libido may be increased from a peak in testosterone

menstrual cycle hormones depicted on a line graph

Luteal Phase

menstrual cycle luteal phase depicted by the changes in the cervix, ovary, and uterus

  • after ovulation, the uterus enters the secretory phase to create the ideal conditions for a fertilized egg

  • the follicle (egg sac) turns into a temporary endocrine organ called the corpus luteum, which secretes progesterone

  • the cervix closes with an impenetrable mucus plug, and cervical fluid dries up

menstrual cycle graphic depicting the cycle hormones in each phase


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