Large intramural fibroids may alter the blood flow to the uterine lining and may also alter the shape of the uterine cavity. Sub serosal fibroids usually don't alter the shape of the uterine cavity, but when large can cause discomfort. These are much less common than the other 2 types of fibroids. Because of their location inside the uterine cavity, sub mucous fibroids can cause fertility problems and miscarriages. http://www.blossomivfindia.com/pages/fibroids-and-fertility