Women in their teens, twenties, and early thirties usually experience regular monthly menstrual cycles. Some people label this time frame “the reproductive years,” but it's important to remember that as long as you ovulate and have periods, you are fertile and you can conceive. For the purposes of this book, therefore, just think of that life stage as that of early adulthood, which lasts, for the average woman, into her forties.

By the time most women reach their late teens, they ovulate regularly, and their bodies establish their “normal” reproductive cycle. Although the length and regularity of the monthly cycle varies from woman to woman, you can think of the typical reproductive cycle as occurring in two main phases:

• Buildup — (follicular phase), the time when the ovaries begin developing a group of follicles, each containing an egg, starting on the first day of menstrual bleeding and continuing until midway through the cycle when one egg has become fully developed and ovulation occurs. This is also the time that the uterine lining begins to thicken again after it is shed with menstruation.

• Premenstrual — (secretory phase), the time following ovulation when the uterine lining matures and prepares for the implantation of a potential fertilized egg.

Every month, through a complex series of hormonal changes, you get ready to be pregnant. Then, if you aren't, you shed the lining of your uterus and start all over again. You know this as your menstrual cycle and, love it or hate it, it has marked the passage of time since the day you started your first period.

Here are some helpful terms for discussing your periods:

• Menstruation, menses, and menorrhea: Terms for the monthly bleeding that you call your period

• Menarche: The beginning of menstruation marked by your first menstrual period

• Amenorrhea: Absence of periods

• Dysmenorrhea: Painful periods

Menarche: The Beginning

In the United States, the average age of a girl's first period is twelve years old, but you may have started anywhere from age eight to age sixteen, and it would still be considered normal. The timing of your first period is determined by a number of things, including whether you were well nourished, the age of your mother's first period, whether you had enough body fat to start the necessary hormone production, and whether you were ill or had certain birth defects. You probably remember the day of your first period and can recall how people around you reacted to the event. This was the beginning of your outlook on menstruation, and even formed some of your ideas about being a woman.

Your Periods

If you are approaching menopause age, you have been having periods for almost thirty years! By now you have formed some pretty strong ideas about what those periods mean to you. Do you call it “The Curse?” Or do you see it as the hallmark of being a woman? What does fertility mean to you? Does it mean monthly pain, or the chance to have your wonderful children? Or both?

You probably have had a cycle somewhere between twenty-one and thirty-five days long, and have bled from four to seven days each time. These fertile years have been a defining part of you for your entire adult life. Fertility can be the cause of pain or joy, sometimes in the same day. As menopause appears on the horizon, you will have to adjust your way of thinking about yourself.

Beyond what your periods mean to you as a woman, you have also learned how they affect your everyday life. Maybe your personality changes during different parts of the month, maybe you are more interested in sex mid-cycle and not at all immediately before your period, or maybe you are even-tempered and easy going all month long. All of these are normal, and by now you can pretty well predict what is normal for you. With the upcoming changes of menopause this may all be turned on its head. You may become unpredictable to yourself, having to learn about your new body and change your expectations of yourself. Something like adolescence, but without the growth spurt.