Leiomyomas, also called "fibroids" or "myomas", are tumors of the muscular wall of the uterus. They are, by definition, benign (not cancers) and are so common that they exist in almost 70% of caucasian women and more than 80% of women of African ancestry by the age of 50. As a result, it is pretty obvious that most of the time leiomyomas don't cause abnormal periods (abnormal uterine bleeding or "AUB") or infertility (difficulty getting pregnant) or any other problem.

Fortunately, we have some idea of the relationship between fibroids and  problems such as AUB or infertility. It seems that the tumor (the fibroid) has to be submucous in location which means that it has to be in contact with, or stretching the endometrial lining in a way that it is difficult for the normal mechanisms in the lining to stop the bleeding when it occurs or to allow an embryo (early pregnancy) to attach and grow. The panel below shows submucous fibroids in an ultrasound and a hysteroscopy image.