How Do Uterine Fibroids Affect Pregnancy Outcomes?

Uterine fibroids, also known as leiomyomas, are benign tumors of the uterus that arise from the smooth muscle tissue of the myometrium. They are among the most common gynecological conditions, affecting up to 70-80% of women by the age of 50 (Stewart, 2015). Fibroids can vary greatly in size, location, and number, and their impact on fertility and pregnancy outcomes depends on these factors. This detailed account explores how different types of uterine fibroids—classified by their location within the uterus—affect a woman’s chances of pregnancy, based on current evidence from the literature.

Classification of Uterine Fibroids

Uterine fibroids are generally classified into four main types based on their location within the uterus:

1. Submucosal fibroids: These are located just beneath the endometrial lining and protrude into the uterine cavity.

2. Intramural fibroids: These develop within the muscular wall of the uterus.

3. Subserosal fibroids: These are located on the outer surface of the uterus and may extend into the pelvic cavity.

4. Pedunculated fibroids: These are attached to the uterine wall by a stalk and can be either submucosal or subserosal (Gupta et al., 2017).

The impact of fibroids on fertility varies depending on their size, number, and location, with submucosal and intramural fibroids being most closely associated with adverse reproductive outcomes.

Impact of Submucosal Fibroids on Pregnancy

Submucosal fibroids are most commonly associated with reduced fertility and adverse pregnancy outcomes due to their direct effect on the endometrial cavity. These fibroids can distort the uterine cavity, interfere with sperm transport, and impede embryo implantation (Pritts et al., 2009). Studies have shown that submucosal fibroids are associated with lower implantation rates, reduced clinical pregnancy rates, and higher miscarriage rates in women undergoing assisted reproductive technologies (ART) such as in vitro fertilization (IVF) (Somigliana et al., 2007).

A systematic review and meta-analysis by Pritts et al. (2009) found that the removal of submucosal fibroids (hysteroscopic myomectomy) significantly improves fertility outcomes, including increased pregnancy and live birth rates, in women with otherwise unexplained infertility. This evidence strongly suggests that submucosal fibroids are detrimental to fertility and that surgical intervention can be beneficial in improving pregnancy chances.

Impact of Intramural Fibroids on Pregnancy

Intramural fibroids are located within the muscular wall of the uterus and are the most common type of fibroid. The impact of intramural fibroids on fertility is more complex and somewhat controversial, as these fibroids do not always distort the uterine cavity (Khan et al., 2014). However, intramural fibroids can still impact pregnancy chances by altering uterine contractility, reducing blood flow to the endometrium, and potentially interfering with embryo implantation (Gupta et al., 2017).

Evidence from the literature suggests that the impact of intramural fibroids on fertility depends largely on their size and proximity to the endometrial cavity. A meta-analysis by Metwally et al. (2012) indicated that intramural fibroids larger than 4 cm are associated with a significant reduction in pregnancy and live birth rates in women undergoing IVF. However, the effect of smaller intramural fibroids is less clear, with some studies suggesting minimal impact on fertility outcomes.

The decision to surgically remove intramural fibroids before attempting conception or ART is often based on the size and number of fibroids, as well as the presence of symptoms such as heavy menstrual bleeding or pelvic pain. Myomectomy, the surgical removal of fibroids, may improve fertility outcomes in selected cases, particularly when large intramural fibroids are present (Khan et al., 2014).

Impact of Subserosal Fibroids on Pregnancy

Subserosal fibroids are located on the outer surface of the uterus and are generally considered to have the least impact on fertility. Because these fibroids do not distort the uterine cavity or directly affect the endometrial lining, they are less likely to interfere with sperm transport, embryo implantation, or early pregnancy maintenance (Somigliana et al., 2007).

Most studies indicate that subserosal fibroids do not significantly reduce pregnancy rates, whether in natural conception or assisted reproductive techniques. For example, a study by Casini et al. (2006) found no significant difference in pregnancy rates between women with subserosal fibroids and those without fibroids undergoing IVF. As a result, surgical removal of subserosal fibroids is not typically recommended solely to improve fertility, unless the fibroids are causing significant symptoms (Casini et al., 2006).

Impact of Pedunculated Fibroids on Pregnancy

Pedunculated fibroids are less common and can be either submucosal or subserosal, depending on their location. The impact of pedunculated fibroids on fertility is similar to that of the base type (submucosal or subserosal). Pedunculated submucosal fibroids, due to their location within the uterine cavity, can interfere with implantation and increase the risk of miscarriage, much like non-pedunculated submucosal fibroids (Pritts et al., 2009).

On the other hand, pedunculated subserosal fibroids, which extend into the pelvic cavity, generally do not affect the uterine cavity and are unlikely to impact fertility. Surgical intervention for pedunculated fibroids is typically reserved for cases where the fibroid is causing symptoms such as pain or pressure, rather than for fertility improvement (Gupta et al., 2017).

Management of Uterine Fibroids in Women Seeking Pregnancy

The management of uterine fibroids in women who are attempting to conceive should be individualized based on the type, size, and number of fibroids, as well as the presence of symptoms and other fertility factors. For submucosal fibroids, hysteroscopic myomectomy is considered the gold standard treatment to improve fertility outcomes. In cases of large intramural fibroids, myomectomy may also be beneficial, particularly if the fibroids are associated with symptoms or are thought to impair implantation (Khan et al., 2014).

The role of medical management, such as the use of gonadotropin-releasing hormone (GnRH) agonists, is primarily to reduce the size of fibroids before surgery or to manage symptoms temporarily. However, these treatments are not generally recommended as long-term solutions for women seeking to conceive, as they do not improve fertility and may delay conception (Stewart, 2015).

Uterine fibroids, depending on their location, size, and number, can significantly affect a woman’s chances of pregnancy. Submucosal fibroids are most detrimental to fertility due to their impact on the uterine cavity, while intramural fibroids may also impair fertility, particularly when large or numerous. Subserosal fibroids are generally less harmful to fertility, and pedunculated fibroids follow the fertility implications of their base type. Management strategies, including surgical removal, are often necessary to optimize fertility outcomes in women with fibroids, particularly when fibroids are symptomatic or significantly interfere with the uterine environment.

References

– Casini ML, Rossi F, Agostini R, Unfer V. Effects of the Position of Fibroids on Fertility. Gynecological Endocrinology. 2006;22(2):106-109.

– Gupta S, Jose J, Manyonda I. Clinical Presentation of Fibroids. Best Practice & Research Clinical Obstetrics & Gynaecology. 2017;34:43-54.

– Khan AT, Shehmar M, Gupta JK. Uterine Fibroids: Current Perspectives. International Journal of Women’s Health. 2014;6:95-114.

– Metwally M, Li TC, Cheong Y. Surgical Treatment of Fibroids for Subfertility. Cochrane Database of Systematic Reviews. 2012;11:CD003857.

– Pritts EA, Parker WH, Olive DL. Fibroids and Infertility: An Updated Systematic Review of the Evidence. Fertility and Sterility. 2009;91(4):1215-1223.

– Somigliana E, Vercellini P, Daguati R, et al. Fibroids and Female Reproduction: A Critical Analysis of the Evidence. Human Reproduction Update. 2007;13(5):465-476.

– Stewart EA. Uterine Fibroids. New England Journal of Medicine. 2015;372(17):1646-1655.