Fibroids are benign lumps of tissue, which grow in the muscular part of the uterus. They are very common – up to 80% of women have at least one fibroid – and increase with age. They are not cancerous or otherwise at all harmful to your health. Uterine fibroids aren’t usually dangerous, however, sometimes, very large fibroids  can cause discomfort and might lead to complications such as anemia (a drop in red blood cells). Anemia causes fatigue from heavy blood loss, and rarely, a transfusion might be needed to counteract the blood loss.