And although some teenagers may find this a difficult topic to address head-on with parents, parents will often be aware, Dr. Jaffray said, not only that their daughters may be missing school, but that they are having to wash bedsheets, or that they are going through sanitary products much faster than expected.

In the first year or two after menarche, the most common reason for heavy or prolonged periods is what is called anovulatory bleeding, reflecting a cycle in which no ovulation has actually occurred, but hormones cause continued bleeding. Over time, cycles should become more regularly ovulatory, and the bleeding should decrease, but in the meantime, the heavy periods can be treated, Dr. Borzutzy said.

Most people who have heavy periods will not actually have bleeding disorders, but about 20 percent of them will, and since some of these disorders are inherited, it is not uncommon to start by diagnosing the problem in the adolescent and move on to finding the same problem in a parent or other family member. “A mother may not recognize her daughter’s heavy menstrual bleeding because it’s just like hers,” Dr. Jaffray said. “Many times we diagnose a young girl and have to go back and encourage the mother or the father to be tested.”

These mothers may have given birth and had difficulties with blood loss, may even have had hysterectomies for their own heavy menstrual bleeding, all without finding out the underlying diagnosis, she said. The Foundation for Women and Girls with Blood Disorders works to raise awareness of these issues and increase the likelihood that medical providers make these diagnoses and treat them appropriately.

In a study published in November in the Journal of Pediatric and Adolescent Gynecology, researchers looked at 258 adolescents who came into the emergency room for heavy menstrual bleeding. Forty-four (17 percent) were admitted to the hospital, and almost a third of those had a bleeding disorder. The mean age of the girls who were hospitalized was 15, and most of them received blood transfusions or other blood products, like platelets or plasma.