Uterine fibroids are common, non-cancerous growths of the uterus that appear during a woman’s childbearing years. Also known as leiomyomas or myomas, these tumors are primarily composed of dense, smooth muscle tissue and vary widely in size and number. While many women with fibroids experience no symptoms, others can face significant issues, including heavy bleeding, pelvic pain, and concerns about their ability to conceive. The relationship between fibroids and impaired fertility depends almost entirely on where the growth is located within the uterine structure, which determines the extent to which the fibroid interferes with conception.
Understanding Uterine Fibroid Locations
Fibroids are classified into three main types based on their position relative to the layers of the uterine wall. The outermost layer is the serosa, the middle muscular layer is the myometrium, and the inner lining is the endometrium.
Subserosal fibroids develop on the outside surface of the uterus, just beneath the serosa layer. These growths expand outward into the pelvic cavity, sometimes forming a stalk (pedunculated fibroid). Intramural fibroids are the most common type, growing directly within the muscular wall (myometrium) of the uterus. They can cause the uterus to enlarge and often result in heavy or prolonged menstrual bleeding. Submucosal fibroids grow just under the endometrium and protrude into the uterine cavity, often causing the most significant symptoms, even when small.
Identifying the High-Risk Types for Infertility
The type of fibroid most strongly associated with infertility and reduced pregnancy rates is the submucosal fibroid. Even small submucosal fibroids can significantly reduce the chances of a successful pregnancy because they directly affect the lining where an embryo must implant. Clinical evidence indicates that women with submucosal fibroids have a substantially lower clinical pregnancy rate. Pregnancy and live birth rates can be reduced by over 60% in women affected by these growths.
Intramural fibroids, which are situated within the muscle wall, represent a secondary concern for fertility. Intramural fibroids that are large or those that significantly distort the uterine cavity are known to decrease pregnancy and implantation rates. Some research suggests that even intramural fibroids that do not distort the cavity may negatively affect fertility. Subserosal fibroids, by contrast, are located on the exterior of the uterus and rarely affect the ability to conceive, as they do not interfere with the uterine cavity or blood flow to the endometrium.
Biological Mechanisms of Conception Interference
The primary way that high-risk fibroids interfere with conception is by physically and biochemically disrupting the environment necessary for embryo implantation. A submucosal fibroid directly compromises the endometrial lining, preventing the fertilized egg from successfully attaching and establishing a blood supply. This physical presence can also alter the shape of the uterine cavity, making the environment unfavorable for the developing embryo.
Fibroids, especially intramural ones, can also affect the uterine muscle’s function, leading to increased or abnormal uterine contractility. This irregular movement can interfere with the transport of sperm and the successful implantation of the embryo. Furthermore, fibroids can create a localized inflammatory and biochemical imbalance within the uterus. This includes a deranged cytokine profile and changes in key molecules necessary for the endometrium to be receptive to an embryo. Fibroids may also cause abnormal vascularization and reduced blood flow to the endometrial tissue, limiting the embryo’s ability to implant and thrive.
Surgical Options to Restore Fertility
For women whose fibroids are identified as the likely cause of their infertility, myomectomy is the standard fertility-sparing surgical procedure. This operation selectively removes the fibroids while preserving the uterus, which is essential for future pregnancy. The choice of surgical technique is determined by the fibroid’s location.
Submucosal fibroids, which protrude into the uterine cavity, are typically removed using a hysteroscopic myomectomy. This minimally invasive approach involves inserting a camera and instruments through the vagina and cervix into the uterus, requiring no external incisions. Intramural fibroids, especially those that are large or multiple, are usually removed via laparoscopic or abdominal myomectomy. Laparoscopic techniques use small incisions and offer a quicker recovery, while abdominal myomectomy uses a larger incision and is reserved for very large or numerous fibroids. Successful removal of fertility-impairing fibroids has been shown to improve pregnancy and live birth rates.