A normal cycle is about 28 days from the first day of bleeding to the first day of the next period. It is also normal for it to be 21 to 35 days. The rise and drop of the hormones progesterone and estrogen cause a period to happen. A rise causes the lining of the uterus to become thin. A drop causes the lining to break down and pass out of the body. This is what causes bleeding. Bleeding often lasts from 3 to 5 days. It is also normal for it to last 7 days. This cycle will happen each month from about 12 years of age to an average age of 51 years of age. The cycle normally only ends with pregnancy or menopause.

Menstrual Flow

Heavy Menstrual Bleeding

Most women lose about 2 ounces of blood or less. Menorrhagia is a loss of more blood than normal. This happens if there is a high volume of blood or a period that lasts more than 7 days. It can be caused by hormone changes or physical problems. The loss of blood can lead to anemia and other health problems.

Absence of Menstruation

Girls may not start to have their period when expected. This is called primary amenorrhea. It is found when a girl does not have a period by:

Age 14 without growth of pubic hair and breasts
Age 16 with or without growth of pubic hair and breasts

Periods may also stop after they have already started. Secondary amenorrhea is when it is absent for at least 3 cycles. It may be caused by:

Pregnancy
Hormonal imbalances
Hypothyroidism
High levels of prolactin in the blood
Eating disorders
Mental health problems
Low or high body fat
Rapid weight loss
Too much exercise
Other health problems

Amenorrhea can lead to problems like a decrease in bone density. It can cause a higher risk of osteoporosis.

Other Types of Abnormal Bleeding

Metrorrhagia—mostly light bleeding in between periods. It may be caused by hormone changes, birth control pill, or infections. It can also be caused by a growth on cervix, uterus or a miscarriage.
Menometrorrhagia—is bleeding in between periods, then bleeding heavily during a period. It may be caused by hormone problems.
Hypomenorrhea—is very light periods. It is often found in female athletes. It can be caused by hormone changes from too much exercise and low weight. It can also be caused by anorexia.
Anovulatory cycle—a specific part of the cycle does not happen. The egg is not released. It can change the cycle and how often the periods happens.

Less common problems are:

Polymenorrhea—too many periods close together (less than 21 days)
Oligomenorrhea—too few cycles (periods far apart)

Some causes of abnormal bleeding are:

Problems during pregnancy
Trauma
Infection
Medicines, such as intrauterine devices (IUDs) and birth control pills
Stress
Treatments and conditions, such as fibroids, polyps, or cancer (rare)

References

Abnormal uterine bleeding. EBSCO DynaMed website. Available at: https://www.dynamed.com/approach-to/abnormal-uterine-bleeding. Updated October 10, 2019. Accessed November 14, 2019.

Amenorrhea. EBSCO DynaMed website. Available at: https://www.dynamed.com/condition/amenorrhea. Updated January 16, 2018. Accessed November 14, 2019.

Bleeding Disorders in Women. US Centers for Disease Control and Prevention website. Available at: https://www.cdc.gov/ncbddd/blooddisorders/women/index.html. Updated April 25, 2018. Accessed November 14, 2019.

Klein DA, Poth MA. Amenorrhea: an approach to diagnosis and management. Am Fam Physician. 2013 Jun 1;87(11):781-788.

Last reviewed September 2019 by EBSCO Medical Review Board Elliot M. Levine, MD, FACOG
Last Updated: 11/20/2020

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