A thick uterus, or endometrial hyperplasia, is caused when a woman's body produces too much estrogen and not enough progesterone, according to the American College of Obstetricians and Gynecologists. Progesterone is a hormone that helps the uterus prepare for pregnancy.
If a woman doesn't ovulate, she doesn't produce progesterone, the American College of Obstetricians and Gynecologists explains. Because of this, the lining of her uterus doesn't shed as it normally would but continues to build up. The cells in the uterine wall not only accumulate but may become abnormal. For some women, this increases their risk of cancer.
Endometrial hyperplasia occurs most often after a woman stops menstruating or in that period before menopause called perimenopause, reports the American College of Obstetricians and Gynecologists. A woman does not ovulate after menopause and during perimenopause and may ovulate only intermittently instead of once a month. Endometrial hyperplasia is also a risk for a woman who is taking a medication that behaves like estrogen in her body or who has polycystic ovary syndrome. It also occurs in women who have not had a hysterectomy but are taking estrogen in high doses, in women who are obese, or in women who are infertile.
Women who are more at risk for endometrial hyperplasia are Caucasian, over 35, began menstruating at an early age and stopped menstruating at a later age, the American College of Obstetricians and Gynecologists explains. Smoking and having a family history of colon or reproductive cancers are also risk factors.