Uterine fibroids, also known as leiomyomas, are non-cancerous growths that develop within the muscular wall of the uterus. These growths are extremely common, affecting a large percentage of women during their reproductive years, though many remain unaware they have them. When a woman is trying to conceive, the presence of fibroids often raises concerns about whether they are interfering with the ability to become pregnant. Their potential to disrupt conception and implantation is determined by their location and size.
Defining Uterine Fibroids and Their Types
Fibroids are the most common benign tumors of the female reproductive tract, composed of smooth muscle cells and fibrous connective tissue. They are estimated to affect up to 80% of women by age 50, but only a fraction of those women experience symptoms or fertility problems. Fibroid development is strongly linked to the hormone estrogen, which is why they typically grow during the childbearing years and often shrink after menopause.
The location of a fibroid is the most telling factor in determining its influence on fertility, leading to three main classifications. Submucosal fibroids grow directly beneath the uterine lining and protrude into the uterine cavity, representing the highest risk for reproductive issues. Intramural fibroids are situated entirely within the muscular wall of the uterus, being the most common type. Subserosal fibroids project outward from the uterine wall, growing on the outer surface of the uterus, and generally have little to no effect on conception.
The Direct Impact on Fertility and Conception
The mere presence of fibroids does not automatically cause infertility, but certain types can significantly reduce the chances of a successful pregnancy. Fibroids are considered the sole cause of infertility in only a small percentage of women, estimated to be around 2% to 3% of cases. The interference is primarily related to mechanical obstruction and the creation of a detrimental environment for an early embryo.
The most profound impact comes from submucosal fibroids, which distort the uterine cavity, interfering with the embryo’s ability to implant into the endometrial lining. These growths can also alter the shape of the uterus, which disturbs the normal wave-like contractions, or peristalsis, of the muscle wall necessary for the transport of sperm and the fertilized egg. Additionally, large fibroids located near the fallopian tubes can cause mechanical compression, physically blocking the pathway where the egg and sperm meet.
Beyond physical blockage, fibroids can create a less receptive environment for implantation through molecular and vascular changes. They can disrupt blood flow in the area just beneath the uterine lining, a process known as aberrant angiogenesis, which is necessary for a healthy pregnancy. Furthermore, fibroids may trigger an inflammatory response and alter the expression of specific genes within the endometrium, directly impacting the window of implantation for the embryo. For intramural fibroids, the risk to fertility increases when they are large, generally defined as greater than four centimeters, even if they do not overtly distort the uterine cavity.
Diagnostic Evaluation for Fibroid-Related Infertility
Identifying fibroids and determining their relationship to infertility requires specialized imaging that maps their size and location. The initial and most common diagnostic tool is a transvaginal ultrasound, which confirms the presence of fibroids and estimates their size and position.
To evaluate the uterine cavity more closely, several specialized procedures may be used:
- Saline Infusion Sonohysterography (SIS): This enhanced ultrasound involves injecting sterile saline solution into the uterus to distend the cavity, providing a clearer outline of the inner lining and any protruding growths, especially smaller submucosal fibroids.
- Hysteroscopy: Considered the definitive method for evaluating the uterine cavity, this minimally invasive procedure involves inserting a thin, lighted telescope through the cervix to examine the inner walls and the openings of the fallopian tubes.
- Magnetic Resonance Imaging (MRI): Used in complex cases involving a very large uterus or multiple fibroids, MRI provides a detailed map of the soft tissues, valuable for surgical planning.
- Hysterosalpingography (HSG): This X-ray procedure uses contrast dye to ensure the fallopian tubes are open and can incidentally identify submucosal growths.
Treatment Strategies to Improve Conception Chances
For patients whose fibroids are confirmed to be the likely cause of their difficulty conceiving, surgical removal is the standard approach aimed at preserving and improving fertility. The procedure to remove fibroids while leaving the uterus intact is called myomectomy. The specific surgical technique depends entirely on the fibroid’s location.
Submucosal fibroids, which are inside the cavity, are typically removed using a hysteroscopic myomectomy, a minimally invasive procedure performed through the vagina and cervix. For intramural or large subserosal fibroids, the surgeon may use a laparoscopic, robotic-assisted, or open abdominal approach. Following a myomectomy, pregnancy rates can range from 40% to 70%, particularly when the fibroids were the only identified factor contributing to infertility.
In some instances, medication like a Gonadotropin-Releasing Hormone (GnRH) agonist may be used temporarily, often for about three months, to shrink the fibroids before surgery. This can make the subsequent myomectomy easier and potentially reduce blood loss during the operation. Other procedures, such as Uterine Artery Embolization (UAE), which shrink fibroids by cutting off their blood supply, are generally not recommended for patients actively seeking conception due to concerns about the long-term effects on uterine health and blood flow to the ovaries.