Uterine fibroids, also called myomas or leiomyomas, are benign (non-cancerous) tumors that arise from the muscle of the uterus. They are extremely common, with most women developing them at some point in time during their life. One study found that by the age of 50, that 70% of Caucasians and 80% of African-Americans will have developed fibroids. There appears to be a genetic link to the development of fibroids, often arising earlier and growing faster in African-Americans. Fibroids often appear to begin when a woman is in her 20s, and usually grow at a slow rate, only reaching a size large enough to cause symptoms when she is in her 30s-40s. Because of this, problematic fibroids are the most common indication for a hysterectomy in women.
When they reach a large enough size, they can cause symptoms such as heavy or irregular bleeding, infertility, pain, or symptoms of “pressure” by pressing on other pelvic organs. However, many fibroids can be totally asymptomatic, with the woman not having any problems until they are incidentally seen by an ultrasound or CT scan.
We classify the location of fibroids as primarily four different types: 1) subserosal- located in the outer-most portion of the wall of the uterus, just underneath the outer surface (the serosa); 2) pedunculated- a type of subserosal fibroid that lies mostly outside of the uterus and only connected by a small stalk of tissue; 3) intramural- found within the main body of uterus; 4) submucosal- In the inner-most portion of the uterus and protruding into the cavity of the uterus. About 55% of fibroids are subserosal or pedunculated; 40% are intramural; and 5% are submucosal. As fibroids increase in size, they may come to span two or more of these categories. Typically, submucosal and larger intramural fibroids are responsible for heavy menstrual bleeding.
So do they affect your chance of conceiving? In short, likely yes, possibly no. This depends on the location and size of fibroids. Many studies have tried to determine the right answers to this question, with some progress being made. Some of the results are still somewhat debated. Many women with fibroids conceive on their own and they may only be discovered during routine pregnancy ultrasounds. However, for many women they can play a role in hindering fertility. It is estimated that fibroids play a role in approximately 5-10% of infertility cases.
There is very good data and it is clear that submucosal fibroids can decrease pregnancy rates by about 35%, and increase miscarriage rates by over 65%. On the other hand, fibroids that are only of the pedunculated or subserosal type appear to have no effect on fertility or miscarriage. Fibroids that are intramural do appear to decrease fertility though the scientific data is less clear. With all categories, however, there likely is an effect of fibroid size and fertility impact. Subserosal fibroids can enlarge to the point that they become predominantly intramural or even submucosal. Once this size, they may also impact fertility.
Both the lowered pregnancy rate and increased miscarriage rate is likely due to altered blood flow within the uterus. The fibroids may serve to divert necessary blood flow away from the uterine cavity where an embryo could implant.
We’ll discuss the treatment options for fibroids in an upcoming blog topic.