What does day 1 of the menstrual cycle signify?

Day 1 of the menstrual cycle signifies the beginning of menstrual discharge, marking the start of a new cycle. This is an important point in understanding the menstrual cycle, as it is used as a reference for tracking the phases within the cycle, including the follicular phase, ovulation, and luteal phase. Menstrual discharge involves the shedding of the uterine lining and the blood from the endometrium, which occurs because an egg from the previous cycle has not been fertilized. Recognizing this as the first day is crucial for calculating the timing of ovulation and understanding the overall cycle length, which is typically about 28 days but can vary significantly among individuals.