Irregularity and heaviness of periods may be due to a number of causes including fibroidsBenign tumours, most often in the uterus. (non-cancerousMalignant, a tumour that may invade surrounding tissues or spread to distant parts of the body. growths) of the wombThe uterus., polypsGrowths on the surface of a mucous membrane (a surface that secretes mucous), lining any body cavity that opens to the outside of the body. (abnormal growth of tissueA group of cells with a similar structure and a specialised function. from the lining of the womb), thickening of the lining of the womb (hyperplasia), adenomyosis of the womb (non-cancerous condition of the womb that often mimics the symptoms of fibroids), bleeding or clotting problems, bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. thinning medication, hormonal imbalance or, very rarely, cancer of the womb or of the neck of the womb (cervixAny neck-like structure; most commonly refers to the neck of the uterus.).