During your menstrual cycle, the lining of your uterus thickens to get ready for pregnancy. Then, during your period, your body sheds the uterus lining along with blood. The amount of blood and fluid lost is usually between 4 and 12 teaspoons each cycle.The average menstrual cycle lasts 28 days (counting from the first day of bleeding to the first day of the next cycle).For some women, though, cycles can be as short as 21 days. For others, they can be as long as 35 days. A normal period lasts between two and seven days.he average menstrual cycle lasts 28 days (counting from the first day of bleeding to the first day of the next cycle). For some women, though, cycles can be as short as 21 days. For others, they can be as long as 35 days.