Menstrual bleeding occurs roughly every 28 days in non-pregnant women. Each month, the uterine lining thickens to prepare for pregnancy. If a woman does not get pregnant, the uterus sheds its lining, causing a monthly period.
Some traits of menstrual bleeding include:
A regular schedule: While the length of time between periods varies among women, most women experience periods around the same time each month.
A predictable bleeding pattern: Every woman’s menstrual bleeding follows its own pattern. For many women, a monthly period begins with light spotting, gets heavier for a day or two, and then gets gradually lighter, ending with spotting.
Time spent not bleeding: Some women with hormonal imbalances or health issues may spot throughout the month. Periods usually last 5-7 days, and never last an entire month.
Menstrual bleeding is often accompanied by other symptoms: In the week or so before a period, changes in hormones can trigger symptoms, such as breast tenderness and headaches. As the uterus contracts to expel the uterine lining as blood, some women experience cramping that can range from mild to intense.
Menstrual blood is usually red: The color can help differentiate a period from spotting, although the blood may be brown at the beginning or end of the period. Some women see large clots or strings of blood with their monthly period, which is less common with spotting.