A thick endometrium may be caused by a condition called endometrial hyperplasia, according to HealthGrades. Due to hormonal problems, endometrial hyperplasia causes abnormal thickening of the uterine lining.
The uterine lining thickens every month to prepare for pregnancy. If pregnancy does not occur, the uterine lining is shed through the process of menstruation. This cycle is controlled by the hormones estrogen and progesterone. These hormones may become imbalanced or unavailable, triggering abnormal cell growth in the uterine lining which in turn causes endometrial hyperplasia, explains HealthGrades.
This condition is most common in women nearing menopause and is usually noncancerous. Symptoms of endometrial hyperplasia include vaginal bleeding, spotting between periods and changes in periods. An accurate diagnosis is achieved through a pelvic examination and laboratory tests conducted by a medical professional, as HealthGrades points out.