When is the first day of a woman's menstrual cycle?
Originally Published: July 25, 2003 - Last Updated / Reviewed On: February 27, 2004
When calculating the length of your menstrual cycle, what is considered to be the actual first day of your cycle? Is it the first day there is "red" bleeding, or does it also include the first day or two of brown discharge?
The start of the menstrual cycle is defined as the first day of bleeding. This includes the day(s) of brown flow before it takes on a more reddish color. Knowing the first day of your cycle is helpful in determining when your next period will arrive, calculating which days are most favorable for pregnancy, and many other topics surrounding your reproductive health.
The brown secretion that many women have towards the beginning and/or end of their cycle is due to the difference in speed of menstrual flow at these times. Often at the start and finish of a woman's period, the rate of her flow is slower than during the in-between time. Delayed flow rate increases the time of exposure of the blood and the uterine lining to oxygen, causing them to darken. This is similar to how a scab browns when the previously red blood is exposed to the air.