Menstruation (also referred to as a “period”) is the name for the monthly bleeding that the majority of healthy women of reproductive age experience. The menstrual cycle lasts from 24 to 35 days, but the average is 28 (meaning there are 28 days from the first day of bleeding to the next first day of bleeding). During the cycle, the lining of the uterus builds up and prepares for a pregnancy. When there is no pregnancy, menstruation occurs, and the lining of the uterus is released in the form of blood and tissue. A cycle of hormones controls the buildup of the uterine lining and the release of fluid. The main reason for a menstrual cycle is to enable a woman to become pregnant.
Earlier we discussed how African American girls often enter puberty earlier than Caucasian girls, so it should come as no surprise that African American girls begin menstruating earlier than Caucasian girls (Herman-Giddens & Slora, 1997). The Add Health data, which we discussed in Chapter 2, enabled researchers to compare racial and ethnic differences in menarche onset. African American and Hispanic girls experienced menarche before the age of 11, whereas Asian girls reached menarche at 14 or later (Adair & Gordon-Larsen, 2001). Girls who have earlier menarche have been found to be shorter and heavier than those who have later menarche, presumably due to the fact that heavier girls have higher estrogen levels (see Sex in Real Life, “Age of Menarche”).
The menstrual cycle can be divided into four general phases: the follicular phase, ovulation, the luteal phase, and the menstrual phase (see Figure 4.5). The follicular phase begins after the last menstruation has been completed and lasts anywhere from 6 to 13 days. Only a thin layer of endometrial cells remains from the last menstruation. As