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by Dr. Jerilynn C. Prior, Scientific Director, Centre for Menstrual Cycle and Ovulation Research

What's Normal?

This is the time from the first period, called menarche, until about age 20. This is a time of maximal physical growth and maturation but also of the social and emotional transition from childhood to young adulthood, from close girl friends to more variable but sometimes permanent attachments with young men. It is also a time of vocational exploration and training.

Menarche is normally between ages 10 and 14 with 12 being a North American average. First periods may be irregular, are often light in flow, and usually do not have cramps. Although it is difficult to remember those early periods, most young women develop cycles that are regularly 20-42 days apart during their first two years after menarche. Although ovulation begins during adolescence, often progesterone levels are low and luteal phase lengths are short. Sometime in the first few years menstrual cramps and some acne develop and then often improve toward the end of adolescence.

What Can Go Wrong?

Women within the first years after menarche may establish long cycles that are over 36 days apart (called oligomenorrhea). Or they may skip periods for many months related to dieting, stress over relationship conflicts, exercise training or rarely illness. It is extremely rare to skip periods for more than six months (amenorrhea).

Women with oligomenorrhea may be at risk for developing anovulatory androgen excess (sometimes called polycystic ovary syndrome) characterized by persistent acne, increased facial, breast and trunk hair, and a tendency to increased weight. The long cycles have normal or high estrogen levels and are almost always anovulatory with low progesterone levels.

Women with amenorrhea are at risk for osteoporosis later in life because they are not building normal bone mineral density during late adolescence. Infertility later in reproductive life caused by ovulation disturbances is more common in women whose weight and height at age 18 gave them a body mass index of over 25.

Women in adolescence, like in perimenopause, may have troubling mood swings, puzzling weight gain, and heavy flow.


The common myth is that with the first period the menstrual cycle and breasts and body shape are now womanly and mature. Rather it takes about 10 years for full maturation to develop.

Another myth is that ovarian cysts mean “polycystic ovary syndrome.” Instead ovarian cysts are common in little girls before in the first period and throughout adolescence. Women on oral contraceptives also commonly have ovarian cysts.

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