Risk Factors Associated With Fibroids

Peter Kovacs, MD, PhD


October 06, 2017

Epidemiology of Uterine Fibroids: A Systematic Review

Stewart EA, Cookson CL, Gandolfo RA, Schultz-Rath R
BJOG. 2017;124:1501-1512


Uterine fibroids are common benign tumors of the uterine smooth muscles. Wide ranges of incidence are reported in the literature. Fibroids may be solitary or multiple and can vary in size. Many of them cause no clinical problems, while in the rest of the cases the symptoms are associated with size and location. Those that grow toward the uterine cavity are more likely to cause bleeding abnormalities and reproductive problems, while those that grow toward the pelvis tend to cause symptoms due to compression of neighboring organs.[1]

Available treatments involve various medical, radiologic, or surgical options. The etiology is likely to be multifactorial; genetic, hormonal, lifestyle, and other unknown factors may be involved.[1]

Because of the frequent diagnosis of uterine fibroids, research addressing their etiology and treatment is important. It is crucial to know their epidemiology and etiologic factors as best as possible. Stewart and colleagues' is the first systematic review that attempts to address these important questions.

Study Summary

This systematic review is based on the findings of 60 papers. Study types vary; both prospective cohort and case-control studies are included. Some papers report the findings of a single center while the majority are registry-based reports.

The method of fibroid diagnosis also significantly varies among the studies; self-report, pelvic exam, imaging studies, and surgical findings have all been used to establish the diagnosis. In most of the studies, the more reliable imaging studies or surgical findings were used.

A wide incidence range of 845-3745 cases per 100,000 women-years is reported in the literature. The incidence is likely to be affected by the population studied or the method of diagnosis. Similarly to the incidence, prevalence varies significantly among the studies, from 4.5% to 68.6%. The reasons for this wide range are likely to be similar.

Thirty categories of risk factors were evaluated, and the following factors were identified as having a reasonably great impact on fibroid growth:

  • Black race is associated with a two- to threefold increased risk.

  • Age is associated with a 10-fold increased risk when those aged 40 years and over or 50 years and over are compared with those aged 20-30 years.

  • Family history is associated with a threefold increased risk.

  • Time since last birth is associated with a two- to threefold increase among those who gave birth more than 5 years ago.

  • Higher parity is associated with a reduced risk (80% risk reduction when those with three or more deliveries are compared with nulliparous women).

  • Uterine fibroids are more common among premenopausal women (three to five times higher risk than in postmenopausal women).

  • Smoking lowers the risk when the BMI is under 22.2 kg/m2 (by one third compared with same-weight nonsmokers)

  • Current use of oral or injectable contraception is associated with a two thirds reduced risk.

  • Women with hypertension are more likely to be diagnosed with fibroids (fivefold increase).

  • The intake of food additives and soybean increases the risk (soybean is associated with 2.5-fold increased risk).


Uterine fibroids are the most common benign tumors affecting women. They may be associated with a variety of symptoms and are the most common cause for hysterectomies. Annually, over 200,000 surgeries are performed for symptomatic fibroids, and the attributed total costs are estimated to be between $5.9 and $34.4 billion USD annually.[1,2] The prevalence and incidence of fibroids are affected by the method of diagnosis. Self-report and pelvic exam are the least specific and are associated with the lowest rates, while imaging studies or surgical findings are likely to result in higher figures due to the identification of small or asymptomatic lesions.

Short- (GnRH agonist/antagonist) and long-term medical (ulipristal acetate) treatment, as well as various radiologic and surgical treatments, are available.[3,4] In order to develop additional safe and effective therapeutic methods, it is important to know how frequent the disease is and which is the best target population to study.

This review reported wide ranges of incidence and prevalence but identified important risk factors. Certain risk factors point to a genetic etiology (black race, family history) while others point to a role of steroid hormones (parity, menopausal status, use of contraception). Steroid hormones are known to play a role in the pathomechanism of fibroid development and growth. The finding that smoking in thin women is associated with a "protective" effect may be confounded by the lower weight and, therefore, lower estradiol levels. The finding that metabolic problems (hypertension, diabetes) are associated with an increased risk could be confounded by higher body mass index and, therefore, higher estradiol levels.

This study has identified important risk factors; these findings can be used well in clinical and research settings.



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