**2. Risk factors**

#### **2.1 Race**

Race constitutes an important risk factor for fibroid development, studies conducted using ultrasound have confirmed that the myoma prevalence is lower in Europe than in the United States, probably due to racial differences (**Figure 1**). In addition to a having greater lifetime incidence of fibroids, black women have fibroids diagnosed at earlier ages, are more likely to be symptomatic and are likely to have different responses to medical treatment than white women [5, 6].

**Figure 1.** *Risk factors.*

#### **2.2 Age**

Age is a significant risk factor for fibroid development. The incidence of pathologically diagnosed fibroids increases with age, reaching its maximum peak at age 50, is negligible before puberty, and also decreases with menopause [7].

#### **2.3 Parity**

Published evidence suggests that pregnancy is a protective factor against fibroid development, due to events that occur at the end of the pregnancy, at delivery or in the postpartum process [8]. Although a direct protective effect of pregnancy has been demonstrated, little is known of the mechanism. It has been suggested that fibroid tissue might be highly susceptible to ischemia during parturition and remodeling [9].

#### **2.4 Genetic factors**

Genetic factors can play an important role in myomas development, the growth of multiple myomas in the same uterus implies that heritage can cause some women to be more predisposed than others [5]. Leiomyomas are monoclonal in origin and 40% of the tumors have karyotypic abnormalities including deletions in chromosome 7, trisomy of chromosome 12 and rearrangements the HMGA1 (6p21) and HGMA2 (12q14) involving genes. Whole exome approaches have identified heterozygous somatic mutations in the mediator complex subunit 12 (MED12) [10]. Alterations of several genes, protooncogenes, signaling pathways and epigenetic mechanisms have been associated with its etiology, some of them are HOXA10, HOXA11, BMP2, among others [7].

Other factors: early menarche, late age for menopause, caffeine and alcohol, family history of uterine fibroids, obesity [1].
