Complaints about the menstrual cycle usually center around irregular cycles, the discomfort of premenstrual syndrome, or painful, heavy periods. Less attention is focused on light or scanty periods, although these are also a menstrual abnormality. Causes of unusually light periods may be related to hormonal changes, the effects of drugs or medical conditions, low body fat or even stress. If you have any abnormalities in your menstrual cycle, including light periods, talk to your doctor.
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Even among women with normal menstrual cycles, flow and cycle length vary. Typical bleeding length ranges from 3 to 7 days, and normal blood loss -- although somewhat difficult to measure -- is between 30 to 50 ml per cycle. Light flow, or hypomenorrhea, is defined as total blood loss less than 30 ml -- or 1 ounce -- per cycle. Women with hypomenorrhea may have regular monthly cycles, or these light, scanty periods may be associated with oligomenorrhea, or infrequent periods. Some women simply have light cycles, and nothing is physically wrong. Light periods can even run in families. But in many cases, there's an explanation for the reduced flow.
Menstruation is controlled by a complex interaction of hormones, and these chemicals regulate the menstrual cycle's rhythm, duration and flow. A light menstrual period is common during hormonal changes, such as the onset of menstruation, or before menopause, when cycles become less frequent, and when flow may be reduced. Light menstrual periods are also a side effect of hormonal birth control methods, such as the birth control pill, hormonal intrauterine devices or implants. These types of birth control cause the endometrial lining in the uterus to be thinner than normal, which leads to less shedding -- and less bleeding -- each month.
Light periods can be related to a variety of health conditions, particularly disorders that also lead to infrequent or absent periods. Menstrual irregularities can be linked to thyroid disorders, including abnormally light periods or an absence of menstruation. A condition known as Asherman syndrome, characterized by uterine scarring, can lead to hypomenorrhea -- which is sometimes the only sign of this condition. Polycystic ovary syndrome (PCOS), a hormonal condition which causes the growth of cysts on the ovaries, leads to menstrual abnormalities which may include light, infrequent or absent periods. Structural abnormalities in the vagina, underdeveloped reproductive organs can also cause menstrual abnormalities.
For normal menstruation to occur, the body needs a certain amount of adipose tissue, or fat. Too little body fat interferes with the production of hormones and can lead to infrequent, absent or unusually light periods. Rapid, significant weight loss caused by dieting, eating disorders, or the physical stress of excessive, strenuous exercise can increase the risk of these menstrual abnormalities. Unusual levels of emotional stress have also been linked to light or irregular periods, at least in the short term, due to the impact of stress on the production of the hormones that regulate the menstrual cycle.
Unusually light periods are not normal, although the cause is typically not serious. However, any changes or abnormalities in your menstrual cycle should be brought to your doctor's attention, since some reasons for light periods may affect fertility or are linked to other conditions that warrant medical attention.
Reviewed by Kay Peck, MPH, RD