The menstrual phase explained

The menstrual phase explained

The menstrual phase is the first phase of the cycle. It starts on the first day of bleeding and lasts until the bleeding stops. During this time the body sheds the uterine lining built up in the previous cycle.

What happens in the body during the menstrual phase

If no fertilization occurs, hormone levels, especially progesterone, drop. As a result the uterine lining can no longer be maintained. The lining breaks down and leaves the body through the vagina as menstrual blood. Menstrual fluid contains blood, mucus and tissue from the uterine lining. This process is a natural part of the cycle and marks the start of a new cycle.

Hormone levels during this phase

During the menstrual phase both estrogen and progesterone are low. These low levels trigger the shedding of the uterine lining. At the same time the brain signals the ovaries to start maturing a new follicle, preparing the body for the next phase of the cycle.

During the menstrual phase some women experience:

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Lower back discomfort

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Lower abdominal cramps caused by contractions of the uterus

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Fatigue or lower energy levels

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Headaches

Why this phase is important

The menstrual phase clears the uterine lining from the previous cycle and resets the body. It allows a new cycle to begin, in which a new egg will mature and the uterine lining will build up again.

Sources and references

Cleveland Clinic, Menstrual Cycle https://my.clevelandclinic.org/health/articles/10132-menstrual-cycle

Cleveland Clinic, Periods and menstrual cycle https://my.clevelandclinic.org/health/articles/3924-periods

Office on Women’s Health, Menstrual cycle https://www.womenshealth.gov/menstrual-cycle