Days 1 to 4 of the menstrual cycle.
On days 1 to 4, the menstrual bleeding occurs, also known as menstruation. This is the shedding of the uterine lining (endometrium) when fertilization has not occurred. During this phase:
- Day 1: The first day of menstrual bleeding marks the beginning of a new cycle. Hormone levels (estrogen and progesterone) are low, and the lining of the uterus begins to shed.
- Day 2: The bleeding continues, and the flow may be moderate to heavy. The body continues to expel the old endometrial lining.
- Day 3: The bleeding usually starts to taper off. The hormone levels remain low, but the body is preparing for the next phase of the cycle.
- Day 4: Light bleeding or spotting may occur. By the end of day 4, the bleeding typically slows significantly, signaling the end of menstruation. The body begins to prepare for the follicular phase, where an egg will mature in the ovaries.
This phase is often accompanied by mild cramps, headaches, and other symptoms as the body adjusts to hormone fluctuations.