The Normal Menstrual Cycle

The lining of the uterus (endometrium) responds to hormones made in the ovary.   The pituitary gland at the base of the brain secretes a hormone called follicle stimulating hormone (FSH) which causes the egg follicles in the ovary to make estrogen.   Estrogen causes the endometrium to thicken.  When ovulation occurs, a second hormone (progesterone) is secreted by the ovary.  This causes the lining of the uterus to become spongy.  The corpus luteum, which makes the progesterone, lasts for fourteen days.  When the progesterone and estrogen levels fall, the endometrium sheds in a menstrual period.

Problems with Ovulation

If ovulation does not occur, the ovary will continue making estrogen, causing the endometrium to keep thickening.  This often leads to a late menstrual period followed by irregular bleeding and spotting.   This can also result in endometrial polyps, or in extreme long-standing cases, cancer of the lining of the uterus. 

Any stress, such as travelling or a new job, can interfere with ovulation.   Fortunately this will usually be temporary, and rarely requires treatment.   Longstanding lack of ovulation is treated with progesterone on a regular basis, which causes the endometrium to shed regularly.  Birth control pills may often accomplish the same goal.  It is usually possible to induce ovulation, but this is reserved for women attempting to become pregnant.   Click here for a simple method of determining ovulation.

Problems with the Uterus

Fibroids

Approximately 30% of women have fibroid tumors.  The medical term for fibroids is leiomyoma, or myoma. These growths are almost always benign, and most of the time do not cause symptoms.  Fibroids typically grow larger as a woman ages, and usually decreases in size after menopause.  They can range in size from pea-size to larger than a grapefruit.  Often a uterus will grow many fibroids.   Click here to learn more about fibroids.

Polyps

Endometrial polyps are growths in the lining of the uterus that are very common, and usually benign.  They usually hang from the lining of the uterus like figs, but at times can be rather flat.  Polyps may result from long-term estrogen stimulation such as occurs from extended periods of not ovulating or from taking estrogen hormones without any progesterone. 

Adenomyosis

When the lining of the uterus grows into the wall of the uterus, the condition is called adenomyosis.  Normally, when the endometrium sheds during a menstrual period the blood is free to drain out through the cervix.  When the lining goes into the muscle some of the blood may be trapped.  When extensive, this may cause severe cramps and heavy bleeding.  This can cause the walls of the uterus to thicken and the uterus to become enlarged.  Often an enlarged uterus from adenomyosis is misdiagnosed as being from fibroids.  Since the treatment of adenomyosis may be different from fibroids, this common error can lead to inappropriate treatment.  Usually ultrasound can tell whether a uterus is enlarged from fibroids or from adenomyosis.



Endometrium has grown into the wall of the uterus.

Other Causes of Abnormal Uterine Bleeding

Although usually a woman will stop having menstrual periods if she is pregnant, bleeding during pregnancy is not uncommon.  If the pregnancy is abnormal, such as a tubal pregnancy or impending miscarriage, the bleeding may be interpreted as being from a menstrual period rather than a complication of pregnancy.  Because pregnancy is such a common cause of abnormal bleeding, a pregnancy test should be among the first tests in anyone who is sexually active, even if she is "sure" she couldn't be pregnant!

Thyroid disorders can cause heavy bleeding, as can disorders in which the blood does not clot normally.  A physician can test for these problems if they are suspected of contributing to the abnormal bleeding.

Other Abnormal Bleeding topics:
Diagnosis
Hysteroscopy
The Resectoscope
Endometrial Ablation
Fibroids
Menopausal Bleeding