Many people wonder what causes an enlarged uterus when they begin to notice pelvic pressure, bloating, or changes in their menstrual cycle. An enlarged uterus can develop for several reasons, and the cause is often related to benign conditions rather than something serious. One of the most common causes is uterine fibroids, which are noncancerous growths that can increase the size of the uterus over time. Adenomyosis, a condition where uterine tissue grows into the muscular wall, can also lead to enlargement and discomfort.