Fibroids are non-cancerous growths in, on, or within the walls of the uterus.
This compression is what causes excessive bleeding during, and occasionally between, menstrual periods. Even small internal fibroids can cause this symptom. If they are growing beneath the outside lining of the uterus, they can become enlarged and put uncomfortable pressure on the pelvis. If they become very large these tumors can also obstruct the fallopian tubes or block implantation of the fertilized egg. Basically, the fibroids begin to take up room on the wall of the uterus, making implantation more difficult.