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How Menstruation Works


Follicular Phase (approx. Day 6 to 14)

Follicular Phase: Part I (approx. Day 6 to 10)

  • The primary follicle continues to develop and grow larger. The antrum gets bigger, and pressure develops inside the follicle. The follicle secretes estrogen at a faster rate.
  • Estrogen levels in the blood rise. The rising estrogen levels will eventually signal the brain that the egg is ready to be released.
  • The rising estrogen levels stimulate growth in the tissue and blood vessels that line the uterus. The uterus lining gets thicker in preparation to receive a fertilized egg.
  • LH and FSH levels remain low but steady, supporting the development of the follicle.

Follicular Phase: Part II (approx. Day 11 to 14 )

  • The primary follicle continues to develop, grow larger and is about ready to be released. The antrum grows, and pressure is near its highest level inside the follicle. The follicle continues to secrete estrogen at a faster rate.
  • Estrogen levels are at their highest, signaling that the egg is ready to be released.
  • LH and FSH levels remain low but steady, supporting the development of the follicle.
  • The uterine lining continues to grow in response to stimulation by estrogen. The mucus plug in the cervix becomes thin and watery.