Uterine fibroids are very rarely cancerous (a type of tumor called leiomyosarcoma happens in fewer than one out of every 1,000 fibroids), but that doesn't mean benign tumors can't cause problems [source: USDHHSOWH]. Only between 10 and 20 percent of women have symptoms, but those who do often experience painful periods, sometimes with heavy bleeding (known as menorrhagia) and clots, bleeding between periods, pain during intercourse, a feeling of fullness or pressure in the lower abdomen and lower back pain [source: GUH-DVIR].
While many uterine fibroids are so small they go unnoticed, some fibroids may grow as big as a grapefruit, or bigger -- those that grow into sizable tumors (several inches in diameter, compared to fibroids that never grow bigger than an apple seed) are rare, and may begin to put the squeeze on some internal organs because of the space they take up, sometimes causing pressure and more frequent and more urgent urination, as well as constipation for some women [source: USDHHSOWH].
The location of the fibroid -- or fibroids, as there could be more than one growing at a time -- may also have a negative impact on a woman's fertility. Some studies show that fibroids may increase complications during pregnancy, including increasing the risk of placental abruption (when the placenta prematurely detaches from the uterine wall) as well as increasing the risk of premature labor and delivery. Women with fibroids are also six times more likely to deliver via cesarean section (C-section) than women without [sources: USDHHSOWH, Puscheck].
Fibroids have also been implicated in conception problems such as implantation failure, as well as an increased risk of miscarriage -- in fact one study found women with fibroids may have as much as a 14 percent risk of miscarriage compared to a 7 percent risk in women without fibroids [source: Lee]. Let's talk more about how and why fibroids may affect a woman's fertility, next.