What is the primary cause of endometrial hyperplasia?

The primary cause of endometrial hyperplasia is anovulation. In a normal menstrual cycle, the balance between estrogen and progesterone is crucial for regulating the growth and shedding of the endometrial lining. Anovulation results in prolonged exposure of the endometrium to estrogen, as there is insufficient progesterone to counteract the effects of estrogen. This unopposed estrogen stimulation leads to excessive growth of the endometrial tissue, resulting in hyperplasia.

In cases where there is inadequate estrogen production, the endometrium would not be stimulated to grow excessively because there would not be enough estrogen present. Excessive progesterone secretion would have the opposite effect by promoting the shedding of the endometrial lining rather than causing hyperplasia. Uterine fibroids may lead to other symptoms and complications but are not considered a primary cause of endometrial hyperplasia by themselves. Thus, anovulation is the most direct factor leading to the unopposed stimulation of the endometrial lining, making it the correct answer.