Abstract

Introduction

Uterine leiomyomas (UL) are slow-growing monoclonal benign neoplasms that develop in several locations in the uterus ¹1. Jolley S. An overview of uterine fibroids. Nurs Standard (Royal College of Nursing) (Great Britain). 2009; 24(6): 44-8. ^{, 2}2. Parker WH. Etiology, symptomatology, and diagnosis of uterine myomas. Fertil Steril 2007; 87(4): 725-36. . They are considered to be the most common tumors in the female reproductive system ³3. Reynolds A. Diagnosis and management of uterine fibroids. Radiol Technol 2007; 79(2): 157-78; 79-82. . Studies performed in the United States have suggested that between 70% and 80% of women aged from 40 to 50 years have UL; however, almost half of these tumors are not even diagnosed, nor do they require treatment, as they do not show clinical signs or symptoms ⁴4. Day Baird D, Dunson DB, Hill MC, Cousins D, Schectman JM. High cumulative incidence of uterine leiomyoma in black and white women: ultrasound evidence. Am J Obstet Gynecol 2003; 188(1):100-7.

5. Schwartz SM, Marshall LM, Baird DD. Epidemiologic contributions to understanding the etiology of uterine leiomyomata. Environ Health Perspec 2000 Oct; 108: 821-7. ^{- 6}6. Divakar H. Asymptomatic uterine fibroids. Best Pract Res Clin Obstet Gynaecol 2008; 22(4): 643-54. .

Although rarely associated with malignization or mortality ⁴4. Day Baird D, Dunson DB, Hill MC, Cousins D, Schectman JM. High cumulative incidence of uterine leiomyoma in black and white women: ultrasound evidence. Am J Obstet Gynecol 2003; 188(1):100-7. ^{, 7}7. Walker CL, Stewart EA. Uterine fibroids: the elephant in the room. Science 2005: 10; 308(5728): 1589-92. , UL can have a significant impact on the quality of life of women of reproductive age⁸. Depending on their anatomical position, number and size, these tumors can cause excessive uterine bleeding and/or a prolonged menstrual period ⁹9. Wegienka G, Baird DD, Hertz-Picciotto I, Harlow SD, Hartmann KE. Uterine leiomyomata (fibroids): are bleeding symptoms more likely to be reported after diagnosis? J Clin Epidemiol 2004; 57 (3): 318-20.

10. Stovall DW. Clinical symptomatology of uterine leiomyomas. Clin Obstet Gynecol 2001; 44(2): 364-71. ^{- 11}11. Wegienka G, Baird DD, Hertz-Picciotto I, Harlow SD, Steege JF, Hill MC et al. Self-reported heavy bleeding associated with uterine leiomyomata. Obstet Gynecol 2003; 101(3): 431-7. ; feeling of pelvic pressure, increase in abdominal volume ¹⁰10. Stovall DW. Clinical symptomatology of uterine leiomyomas. Clin Obstet Gynecol 2001; 44(2): 364-71. ^{, 12}12. Taylor E, Gomel V. The uterus and fertility. Fertil Steril 2008; 89(1): 1-16. ^{, 13}13. Bukulmez O, Doody KJ. Clinical features of myomas. Obstet Gynecol Clin North Am 2006; 33(1): 69-84. ; pain during sexual intercourse ¹⁴14. Lippman SA, Warner M, Samuels S, Olive D, Vercellini P, Eskenazi B. Uterine fibroids and gynecologic pain symptoms in a population-based study. Fertil Steril 2003; 80(6): 1488-94. and urinary incontinence ¹⁵15. Waetjen LE, Dwyer PL. Estrogen therapy and urinary incontinence: what is the evidence and what do we tell our patients? Int Urogynecol J Pelvic Floor Dysfunct 2006; 17(5): 541-5. ^{, 16}16. Waetjen LE, Liao S, Johnson WO, Sampselle CM, Sternfield B, Harlow SD et al. Factors associated with prevalent and incident urinary incontinence in a cohort of midlife women: a longitudinal analysis of data: study of women's health across the nation. Am J Epidemiol 2007; 165(3): 309-18. . Additionally, the UL can have a negative impact on the reproductive function and it is associated with infertility and adverse gestational outcomes, such as spontaneous abortions, fetal anomalies, premature births, and a higher number of indications for Cesarean sections ¹⁰10. Stovall DW. Clinical symptomatology of uterine leiomyomas. Clin Obstet Gynecol 2001; 44(2): 364-71. ^{, 17}17. Coronado GD, Marshall LM, Schwartz SM. Complications in pregnancy, labor, and delivery with uterine leiomyomas: a population-based study. Obstet Gynecol 2000; 95(5): 764-9.

18. Biderman-Madar T, Sheiner E, Levy A, Potashnik G, Mazor M. Uterine leiomyoma among women who conceived following fertility treatment. Arch Gynecol Obstet 2005; 272(3): 218-22.

19. Ouyang DW, Economy KE, Norwitz ER. Obstetric complications of fibroids. Obstet Gynecol Clin North Am 2006; 33(1): 153.

20. Klatsky PC, Tran ND, Caughey AB, Fujimoto VY. Fibroids and reproductive outcomes: a systematic literature review from conception to delivery. Am J Obstet Gynecol 2008; 198(4): 357-66.

21. Khaund A, Lumsden MA. Impact of fibroids on reproductive function. Best Pract Res Clin Obstet Gynaecol 2008; 22(4): 749-60. ^{- 22}22. George L, Granath F, Johansson ALV, Olander B, Cnattingius S. Risks of repeated miscarriage. Paediatric Perinatal Epidemiol 2006; 20(2): 119-26. .

Epidemiological data on risk factors for the development of UL primarily originate from studies conducted in the United States. In these studies, higher frequencies of tumors stood out among black women^4,23-26, those exposed to factors associated with the increase in ovarian hormones (estrogen and progesterone), those undergoing hormonal therapy ²⁷27. Reed SD, Cushing-Haugen KL, Daling JR, Scholes D, Schwartz SM. Postmenopausal estrogen and progestogen therapy and the risk of uterine leiomyomas. Menopause 2004; 11(2): 214-22. , those consuming greater amounts of red meat and sausages ²⁸28. Chiaffarino F, Parazzini F, La Vecchia C, Chatenoud L, Di Cintio E, Marsico S. Diet and uterine myomas. Obstet Gynecol 1999; 94(3): 395-8. , those aged between 40 and 50 years ⁴4. Day Baird D, Dunson DB, Hill MC, Cousins D, Schectman JM. High cumulative incidence of uterine leiomyoma in black and white women: ultrasound evidence. Am J Obstet Gynecol 2003; 188(1):100-7. ^{, 29}29. Wise LA, Palmer JR, Adams-Campbell LL, Rosenberg L. Age-specific incidence rates for uterine leiomyomata in the Black Women's Health Study. Am J Epidemiol 2004; 159(S11): 92-S. , those who had had an early menarche ³⁰30. Marshall LM, Spiegelman D, Goldman MB, Manson JE, Colditz GA, Barbieri RL et al. A prospective study of reproductive factors and oral contraceptive use in relation to the risk of uterine leiomyomata. Fertility Sterility 1998; 70(3): 432-9.

31. Wise LA, Palmer JR, Harlow BL, Spiegelman D, Stewart EA, Adams-Campbell LL et al. Reproductive factors affected the risk of uterine leiomyomata in African-American women. Evid Based Obstet Gynecol 2004; 6(3): 125-6. ^{- 32}32. Cooper R, Hardy R, Kuh D. Timing of menarche, childbearing and hysterectomy risk. Maturitas 2008; 61(4): 317-22. , those with a high BMI ³¹31. Wise LA, Palmer JR, Harlow BL, Spiegelman D, Stewart EA, Adams-Campbell LL et al. Reproductive factors affected the risk of uterine leiomyomata in African-American women. Evid Based Obstet Gynecol 2004; 6(3): 125-6. ^{, 33}33. Marshall LM, Spiegelman D, Manson JE, Goldman MB, Barbieri RL, Stampfer MJ et al. Risk of uterine leiomyomata among premenopausal women in relation to body size and cigarette smoking. Epidemiology 1998; 9(5): 511-7.

34. Wise LA, Palmer JR, Spiegelman D, Harlow BL, Stewart EA, Adams-Campbell LL et al. Influence of body size and body fat distribution on risk of uterine leiomyomata in U.S. black women. Epidemiology 2005;16(3): 346-54.

35. Terry KL, Missmer SA, Hankinson SE, Willett WC, De Vivo I. Lycopene and other carotenoid intake in relation to risk of uterine leiomyomata. Am J Obstet Gynecol 2008;198(1). ^{- 36}36. Parazzini F. Risk factors for clinically diagnosed uterine fibroids in women around menopause. Maturitas 2006; 55(2):174-9. and fat percentage ³⁷37. Sato F, Nishi M, Kudo R, Miyake H. Body fat distribution and uterine leiomyomas. J Epidemiol / Japan Epidemiological Association 1998; 8(3): 176-80. , and those with an increase in weight during adulthood ³³33. Marshall LM, Spiegelman D, Manson JE, Goldman MB, Barbieri RL, Stampfer MJ et al. Risk of uterine leiomyomata among premenopausal women in relation to body size and cigarette smoking. Epidemiology 1998; 9(5): 511-7. ^{, 34}34. Wise LA, Palmer JR, Spiegelman D, Harlow BL, Stewart EA, Adams-Campbell LL et al. Influence of body size and body fat distribution on risk of uterine leiomyomata in U.S. black women. Epidemiology 2005;16(3): 346-54. ^{, 38}38. Terry KL, De Vivo I, Hankinson SE, Spiegelman D, Wise LA, Missmer SA. Anthropometric characteristics and risk of uterine leiomyoma. Epidemiology 2007; 18(6): 758-63. . On the other hand, lower frequencies of tumors were found in women who practiced physical activities ³⁹39. Baird DD, Dunson DB, Hill MC, Cousins D, Schectman JM. Association of physical activity with development of uterine leiomyoma. Am J Epidemiol 2007; 165(2): 157-63. , smokers ³⁰30. Marshall LM, Spiegelman D, Goldman MB, Manson JE, Colditz GA, Barbieri RL et al. A prospective study of reproductive factors and oral contraceptive use in relation to the risk of uterine leiomyomata. Fertility Sterility 1998; 70(3): 432-9. ^{, 33}33. Marshall LM, Spiegelman D, Manson JE, Goldman MB, Barbieri RL, Stampfer MJ et al. Risk of uterine leiomyomata among premenopausal women in relation to body size and cigarette smoking. Epidemiology 1998; 9(5): 511-7. ^{, 40}40. Samadi AR, Lee NC, Flanders WD, Boring JR, Parris EB. Risk factors for self-reported uterine fibroids: A case-control study. Am J Public Health 1996; 86(6): 858-62. ^{, 41}41. Chen CR, Buck GM, Courey NG, Perez KM, Wactawski-Wende J. Risk factors for uterine fibroids among women undergoing tubal sterilization. Am J Epidemiol 2001; 153(1): 20-6. , those with a higher number of children ³⁰30. Marshall LM, Spiegelman D, Goldman MB, Manson JE, Colditz GA, Barbieri RL et al. A prospective study of reproductive factors and oral contraceptive use in relation to the risk of uterine leiomyomata. Fertility Sterility 1998; 70(3): 432-9. ^{- 31}31. Wise LA, Palmer JR, Harlow BL, Spiegelman D, Stewart EA, Adams-Campbell LL et al. Reproductive factors affected the risk of uterine leiomyomata in African-American women. Evid Based Obstet Gynecol 2004; 6(3): 125-6. ^{, 36}36. Parazzini F. Risk factors for clinically diagnosed uterine fibroids in women around menopause. Maturitas 2006; 55(2):174-9. ^{, 42}42. Wise LA, Palmer JR, Harlow BL, Spiegelman D, Stewart EA, Adams-Campbell LL et al. Reproductive factors, hormonal contraception, and risk of uterine leiomyomata in African-American women: a prospective study. Am J Epidemiol 2004; 159(2): 113-23. , those who had reached menopause ³⁶36. Parazzini F. Risk factors for clinically diagnosed uterine fibroids in women around menopause. Maturitas 2006; 55(2):174-9. and those who consumed greater amounts of fruits, vegetables and fish ²⁸28. Chiaffarino F, Parazzini F, La Vecchia C, Chatenoud L, Di Cintio E, Marsico S. Diet and uterine myomas. Obstet Gynecol 1999; 94(3): 395-8. ^{, 35}35. Terry KL, Missmer SA, Hankinson SE, Willett WC, De Vivo I. Lycopene and other carotenoid intake in relation to risk of uterine leiomyomata. Am J Obstet Gynecol 2008;198(1). .

Whereas studies conducted in the United States indicate prevalences of up to 80%, depending on the characteristics of the sub-groups studied, European studies have revealed significantly lower prevalences of tumors ⁴³43. Payson M, Leppert P, Segars J. Epidemiology of myomas. Obstet Gynecol Clin North Am 2006; 33(1):1. . In Germany, 10.7% of participants of a study performed with 10,241 women aged less than 65 years reported having received a diagnosis of “benign tumor in the uterus” ⁴³43. Payson M, Leppert P, Segars J. Epidemiology of myomas. Obstet Gynecol Clin North Am 2006; 33(1):1. ^{, 44}44. Heinemann K, Thiel C, Mahner S, Lewis MA, Raff T, ahl-Habich D, et al. Benign gynecological tumors: Estimated incidence: Results of the German Cohort Study on Women's Health. Eur J Obstet Gynecol Reprod Biol 2003; 107(1): 78-80. . In Italy, UL cases were detected by ultrasound in 21.4% of participants of a study conducted with 341 women aged between 30 and 60 years ⁴⁵45. Marino JL, Eskenazi B, Warner M, Samuels S, Vercellini P, Gavoni N et al. Uterine leiomyoma and menstrual cycle characteristics in a population-based cohort study. Hum Reprod 2004; 19(10): 2350-5. . In Sweden, these tumors were also diagnosed by ultrasound in 3.3% of women aged from 25 to 32 years and in 7.8% of those aged from 33 to 40 years in a random sample comprised of 335 women ⁴⁶46. Borgfeldt C, Andolf E. Transvaginal ultrasonographic findings in the uterus and the endometrium: low prevalence of leiomyoma in a random sample of women age 25-40 years. Acta Obstet Gynecol Scand 2000; 79 (3): 202-7. .

In Brazil, there are few epidemiological data on UL. At present, only one study has been identified, which was conducted with a low-income population cared for in a health clinic of the city of São Paulo. In this study, UL was found in 23% of white women and 42% of black ones. The occurrence of hysterectomy for UL also varied between groups, totaling 4% among white women and 16% among black ones ⁴⁷47. Souza VC. A prevalência de miomas uterinos em mulheres negras: as dificuldades e avanços e análise dos dados com recorte racial. O livro da saúde da mulher negra: nossos passos vêm de longe . Rio de Janeiro: Pallas/Criola/Global Exchange; 2000. p. 88-118. .

Several reasons indicate the need for better identification of the characteristics of occurrence of this condition among Brazilian women. UL has a great negative impact on women's health, whether due to the reduction in the quality of life of a significant number of young women of reproductive age ⁸8. Flake GP, Andersen J, Dixon D. Etiology and pathogenesis of uterine leiomyomas: a review. Environ Health Perspect 2003; 111(8): 1037-54. or due to the increase in the number of mutilating surgeries³. Not less important are the differences between the Brazilian and American contexts, especially with regard to ethnic relations and their interfaces with the remaining demographic and socioeconomic characteristics ⁴⁸48. Travassos C, Williams DR. The concept and measurement of race and their relationship to public health? A review focused on Brazil and the United States. Cad Saúde Pública 2004: 20(3): 660-78. .

Contrasting this lack of evidence, there is growing space for reflection and social policies aimed at women in general and, specifically, the African Brazilian population ⁴⁹49. Maio MC, Monteiro S. Tempos de racialização: o caso da ‘saúde da população negra' no Brasil. Hist Ciênc Saúde Manguinhos 2005; 12(2): 419-46. ^{, 50}50. BRASIL. II Plano Nacional de Políticas para as Mulheres. Brasília: Secretaria Especial de Políticas para as Mulheres . Presidência da República; 2008. . Governmental policies have sought, mainly in the last decade, “to increase, qualify and humanize comprehensive care for women's health in the Sistema Único de Saúde (SUS – Unified Health System) […] aiming to reduce female morbidity and mortality […], considering ethnic peculiarities” ⁵⁰50. BRASIL. II Plano Nacional de Políticas para as Mulheres. Brasília: Secretaria Especial de Políticas para as Mulheres . Presidência da República; 2008. .

In this sense, special attention has been given to the most frequent diseases and conditions found in the black population, among which is UL ⁴⁹49. Maio MC, Monteiro S. Tempos de racialização: o caso da ‘saúde da população negra' no Brasil. Hist Ciênc Saúde Manguinhos 2005; 12(2): 419-46. .

Thus, aiming to contribute to the knowledge about epidemiology of UL, the present study was conducted with women participating in the Pró-Saúde Study and had the purpose of estimating the prevalence of (1) cases of self-reported medical diagnosis of UL; (2) cases of self-reported medical diagnosis of UL, with symptoms prior to diagnosis; and (3) cases of self-reported medical diagnosis of UL, with the performance of hysterectomy. Additionally, the prevalences of these three outcomes were identified in different demographic and socioeconomic strata and according to access to and use of health services.

Methods

The Pró-Saúde Study

The Pró-Saúde Study is a longitudinal investigation conducted among technical-administrative workers of a university located in the city of Rio de Janeiro, Southeastern Brazil. The social determinants of health and health behavior are its main thematic focus. All active workers found in the institution at the beginning of the study (1999) were invited to participate ⁵¹51. Faerstein E, Chor D, Lopes CS, Werneck GL. The Pro-Saude Study: general characteristics and methodological aspects. Rev Bras Epidemiol 2005; 8(4): 454-66. .

Study population

Cross-sectional data on the female population participating in the two stages of the baseline of the Pró-Saúde Study, conducted in 1999-2001, were used in the analyses of this study. The eligible population was comprised of 2,466 workers; of these, 1,819 (73.8%) participated in the two stages of the baseline of this study. A total of 1,733 workers were analyzed after excluding those who did not provide information about the medical diagnosis of UL (n = 86); in general, the latter had poorer socioeconomic conditions, compared to those analyzed in the present study.

Data collection and study variables

Self-administered questionnaires were applied in the workplace by trained field researchers, assisted by supervisors. Questions about the following aspects were included: socioeconomic conditions, gender, ethnic group, geographic and social mobility, experience of discrimination, work-related stress, social support and network patterns, women's health, morbidities, work accidents, work-related behavioral disorders and common mental disorders. Methods used to improve the quality of information, such as pilot studies, validation of scales and test-retest reliability tests, were performed ⁵¹51. Faerstein E, Chor D, Lopes CS, Werneck GL. The Pro-Saude Study: general characteristics and methodological aspects. Rev Bras Epidemiol 2005; 8(4): 454-66. .

Outcome

Information about the medical diagnosis of UL was obtained from participants in 1999 through the following question: “Have you ever been informed by a physician that you had uterine leiomyoma, a benign tumor in the uterus?”. The test-retest reliability of responses was assessed in a stratified sample (age and level of education) of 98 women who were not eligible for the Pró-Saúde Study (temporary workers of the same university), with an interval of two weeks, and it was considered to be excellent ( kappa = 0.94 – 95%CI: 0.86; 1.00).

Additionally, participants provided information about age of diagnosis of UL, previous symptoms and performance of hysterectomy as a result of UL. Based on this information, three case definitions were developed and explored separately as outcomes of interest, and the second and third definitions were a sub-set of the first one: (1) totality of cases of self-reported medical diagnosis of UL; (2) cases of self-reported medical diagnosis of UL, with symptoms prior to diagnosis; and (3) cases of self-reported medical diagnosis of UL, with the performance of hysterectomy.

Socioeconomic and demographic variables

Age: discrete variable categorized in two ways: (1) younger than 35 years, from 35 to 44 years, from 45 to 54 years, and older than 54 years; and (2) younger than 45 years, and 45 years and older.

Color/race: in 1999, information about participants' color/race was collected with the open question (“In your opinion, what is your color/race?”). A total of 41 distinct terms were reported to identify participants' color/race (including men). These terms were categorized as follows: white, brown (typical Portuguese words such as parda, morena, mulata, mestiça and cabocla were used to describe mixed ethnicity), black (typical Portuguese words such as negra, preta, Africana and escura were used to describe mixed ethnicity) and of Asian descent ⁵²52. Maio MC, Monteiro S, Chor D, Faerstein E, Lopes CS. [Ethnicity/race in the Pro-Saude Study: comparative results of two methods of self-classification in Rio de Janeiro, Brazil]. Cad Saúde Pública 2005; 21(1): 171-80. . Participants of Asian descent were excluded from the analyses due to their small number (n = 8; - 0.5%).

Level of education: complete primary school, complete secondary school, and complete university undergraduate level or higher.

Per capita household income: variable obtained by dividing the total income of those contributing to the household expenses by the number of residents. It was categorized into: less than three minimum wages (MW), three to six MW, and more than six MW (One MW was R$136.00 or US$ 71.57 at the time of this study).

Variables markers of health service access and use

Pap smear test: has never had it performed or had it performed more than three years before, and had it performed less than three years before.

Breast examination (gynecologist): has never had a breast examination performed or had it more than three years before, and had it performed less than three years before.

Health insurance: yes and no.

Statistical analyses

Prevalences and their 95% confidence intervals (95%CI) were estimated for the three outcomes in the entire study population in demographic, socioeconomic and health service access and use strata. Prevalences were also stratified according to age groups (younger than 45 years, 45 years and older). The cut-off point was defined after changes in the pattern of prevalences were verified close to the age of 45 years in the population studied. Pearson's chi-square test was used to assess the heterogeneity of proportions of sub-groups. Differences with a p-value < 0.05 were considered to be statistically significant.

Data entry and consistency checking were performed with the Epi-Info software. Analyses were made in the R statistical software, version 2.6.2. The present study was approved by the Research Ethics Committee of the University of the State of Rio de Janeiro. There were no conflicts of interest.

Results

Of all 1,733 study participants, 72% were younger than 45 years, 51.9% reported they were white, 62.4% had health insurance, 88.4% had a Pap smear test performed less than three years before and 88.1% had a breast examination performed less than three years before. Slightly less than half (46%) reported they had completed their university undergraduate program and 37% had a per capita household income higher than six MW ( Table 1 ).

The prevalence of medical diagnosis of UL was 23.3% (95%CI - 21.3; 25.3), that of UL with symptoms prior to diagnosis was 13.3% (95%CI - 11.7; 15.0), and that of hysterectomy due to tumor was 8.4% (95%CI - 7.5; 10.3). Figure 1 shows the prevalences of three outcomes according to age groups. There was an increase in the prevalences with the increase in age until 45 years, with a subsequent stabilization after this age ( Figure 1 ).

Table 2 shows the prevalences of three outcomes among the sub-groups formed by the demographic, socioeconomic and health service access and use strata. With regard to the medical diagnosis of UL, apart from the increase in prevalence with age, there were also higher prevalences among black women (32.8% - p < 0.001), those who had completed primary education (33.8% - p < 0.001) and those who had had a breast examination less than three years before (24% - p = 0.021).

This pattern of distribution of prevalences in the strata of covariables was similar to other two outcomes (UL with symptoms prior to diagnosis and cases of hysterectomy due to UL). In both cases, higher prevalences were also found among women with a lower per capita household income (19.7% of those with symptoms prior to diagnosis and 14.3% of cases of hysterectomy due to UL, each with p < 0.001) and among those who did not have health insurance (16.6% of those with symptoms prior to diagnosis, with p = 0.002; and 11.3% of cases of hysterectomy due to UL, with p = 0.007). Differences were not statistically significant according to time of performance of breast examination ( Table 2 ).

Table 3 shows the prevalences of UL by covariables, stratified by age for the three outcomes. Considering the two age groups analyzed, the patterns found were different. Black women and those who had completed primary education had significantly higher prevalences of medical diagnosis of UL in the stratum of women younger than 45 years exclusively (25.6% - p < 0.001 and 25.4% - p = 0.013, respectively). On the other hand, women aged 45 years and more, who had had the Pap smear test and breast examination less than three years before, showed higher prevalences (40.2% - p = 0.023 and 40.8% - p = 0.007, respectively). The remaining variables were not significantly different in both age groups ( Table 3 ).

Stratifications of prevalences by age also showed different patterns for UL with symptoms prior to diagnosis. Being black and having a per capita household income lower than three MW were directly associated with the diagnosis of symptomatic UL among women younger than 45 years (13.5% - p = 0.006, and 15% - p = 0.002, respectively). In contrast, those aged 45 years and more showed no statistically significant differences with regard to the characteristics studied ( Table 3 ).

Concerning cases of hysterectomy due to UL, the same variables were associated with higher prevalences among women younger than 45 years. There were no statistically significant differences with regard to the characteristics studied among women aged 45 years and more ( Table 3 ).

Discussion

The prevalences of UL reported in the international literature show great variation: from 3.3% in a Swedish study ⁴⁶46. Borgfeldt C, Andolf E. Transvaginal ultrasonographic findings in the uterus and the endometrium: low prevalence of leiomyoma in a random sample of women age 25-40 years. Acta Obstet Gynecol Scand 2000; 79 (3): 202-7. to 80% in an American study⁴4. Day Baird D, Dunson DB, Hill MC, Cousins D, Schectman JM. High cumulative incidence of uterine leiomyoma in black and white women: ultrasound evidence. Am J Obstet Gynecol 2003; 188(1):100-7., depending on the geographic origin and age group of the population analyzed³3. Reynolds A. Diagnosis and management of uterine fibroids. Radiol Technol 2007; 79(2): 157-78; 79-82. ^{, 4}4. Day Baird D, Dunson DB, Hill MC, Cousins D, Schectman JM. High cumulative incidence of uterine leiomyoma in black and white women: ultrasound evidence. Am J Obstet Gynecol 2003; 188(1):100-7.. As many cases of UL are asymptomatic, the methods used to estimate the frequency of tumors can also influence these results ⁵5. Schwartz SM, Marshall LM, Baird DD. Epidemiologic contributions to understanding the etiology of uterine leiomyomata. Environ Health Perspec 2000 Oct; 108: 821-7. . Thus, studies based on the previous diagnosis of UL can generate underestimated prevalences, as asymptomatic cases among participants without a history of diagnosis will probably pass unnoticed, especially if they do not have adequate access to health services ⁵5. Schwartz SM, Marshall LM, Baird DD. Epidemiologic contributions to understanding the etiology of uterine leiomyomata. Environ Health Perspec 2000 Oct; 108: 821-7. . On the other hand, this underestimation decreases in studies that use ultrasound tests, for example.

The prevalences estimated in the present study are in an intermediate position, closer to the American estimates. One must take into consideration the fact that the history of medical diagnosis of UL was reported by participants and that, consequently, these data are subject to underestimation, due to the existence of asymptomatic cases. Some strategies were used to minimize this limitation. The first one, although indirect, was the assessment of reliability of the question about the diagnosis of UL, which indicated an excellent pattern. The second one was the exploration of the three outcomes, which, apart from enabling the assessment of the severity of UL, tested different levels of specificity of information about tumors reported. The third one was the use of variables markers of access to health services in the analyses. In this sense, a great part of the study population had reasonable conditions of obtaining a medical diagnosis of tumors, although asymptomatic, as they had health insurance and had had a Pap smear test and breast examination performed less than three years before.

On the other hand, as workers excluded from the analyses, as a result of their not providing information about UL, had a poorer socioeconomic profile than participants, the prevalences of UL, symptomatic UL and hysterectomy due to UL were probably underestimated.

As in other studies, the prevalences of UL increased with age ⁴4. Day Baird D, Dunson DB, Hill MC, Cousins D, Schectman JM. High cumulative incidence of uterine leiomyoma in black and white women: ultrasound evidence. Am J Obstet Gynecol 2003; 188(1):100-7.

5. Schwartz SM, Marshall LM, Baird DD. Epidemiologic contributions to understanding the etiology of uterine leiomyomata. Environ Health Perspec 2000 Oct; 108: 821-7. ^{- 6}6. Divakar H. Asymptomatic uterine fibroids. Best Pract Res Clin Obstet Gynaecol 2008; 22(4): 643-54. . Epidemiological studies have found higher frequencies of tumors in women aged between 40 and 50 years, thus strengthening the hypothesis of the role of hormonal imbalance in their development. According to this hypothesis, UL tumors would result from an excess of blood estrogen and progesterone; thus, the longer one is exposed to this imbalance, the greater the chance of developing tumors ²2. Parker WH. Etiology, symptomatology, and diagnosis of uterine myomas. Fertil Steril 2007; 87(4): 725-36. ^{, 7}7. Walker CL, Stewart EA. Uterine fibroids: the elephant in the room. Science 2005: 10; 308(5728): 1589-92. .

Despite the cross-sectional design of this study, the results suggest that age is a possible modifier of the association between UL and the remaining variables analyzed, as the pattern of distribution of prevalences varied in the demographic, socioeconomic and health service access and use sub-groups according to the age group analyzed. Significant differences were more frequent among women younger than 45 years. In this group, the greatest prevalences were found among black participants and those with poorer socioeconomic conditions.

On the other hand, women aged 45 years and more did not show significant differences in estimates, according to their demographic and socioeconomic pattern. Higher prevalences were only found among those who reported having greater access to medical diagnosis, i.e. Pap smear test and breast examination performed less than three years before.

The remaining results corroborate the findings of studies performed in the United States with women from different color/race groups. According to these studies, compared to white women, tumors in black women occur between two and nine times more frequently in all age groups, in addition to the higher number of tumors, more severe symptoms, younger ages when diagnosed, and higher rates of hysterectomy ⁴4. Day Baird D, Dunson DB, Hill MC, Cousins D, Schectman JM. High cumulative incidence of uterine leiomyoma in black and white women: ultrasound evidence. Am J Obstet Gynecol 2003; 188(1):100-7. ^{, 23}23. Marshall LM, Spiegelman D, Barbieri RL, Goldman MB, Manson JE, Colditz GA et al. Variation in the incidence of uterine leiomyoma among premenopausal women by age and race. Obstet Gynecol 1997; 90 (6): 967-73.

24. Huyck KL, Panhuysen CI, Cuenco KT, Zhang J, Goldhammer H, Jones ES et al. The impact of race as a risk factor for symptom severity and age at diagnosis of uterine leiomyomata among affected sisters. Am J Obstet Gynecol 2008; 198 (2): 168 e1-9.

25. Weiss G, Noorhasan D, Schott LL, Powell L, Randolph JF, Johnston JM. Racial differences in women who have a hysterectomy for benign condition. Womens Health Issues 2009; 19(3): 202-10. ^{- 26}26. Faerstein E, Szklo M, Rosenshein N. Risk factors for uterine leiomyoma: a practice-based case-control study. I. African-American heritage, reproductive history, body size, and smoking. Am J Epidemiol 2001; 153(1): 1-10. ^{, 53}53. Kjerulff KH, Erickson BA, Langenberg PW. Chronic gynecological conditions reported by US women: Findings from the National Health Interview Survey, 1984 to 1992. Am J Public Health 1996; 86(2): 195-9. ^{, 54}54. Wise LA, Palmer JR, Stewart EA, Rosenberg L. Age-specific incidence rates for self-reported uterine leiomyomata in the Black Women's Health Study. Obstet Gynecol 2005; 105(3): 563-8. . However, the causes of ethnic inequality in the occurrence of UL remain unknown and possible explanatory mechanisms have been scarcely studied in the literature.

Epidemiological studies suggest that risk factors established for these tumors, such as those associated with reproductive life and lifestyle, could only explain a small fraction of color/race inequalities ⁴4. Day Baird D, Dunson DB, Hill MC, Cousins D, Schectman JM. High cumulative incidence of uterine leiomyoma in black and white women: ultrasound evidence. Am J Obstet Gynecol 2003; 188(1):100-7. ^{, 23}23. Marshall LM, Spiegelman D, Barbieri RL, Goldman MB, Manson JE, Colditz GA et al. Variation in the incidence of uterine leiomyoma among premenopausal women by age and race. Obstet Gynecol 1997; 90 (6): 967-73. ^{, 26}26. Faerstein E, Szklo M, Rosenshein N. Risk factors for uterine leiomyoma: a practice-based case-control study. I. African-American heritage, reproductive history, body size, and smoking. Am J Epidemiol 2001; 153(1): 1-10. . Marshall et al, for example, found a relative risk for UL of 3.25 (95%CI 2.71; 3.88) and that of hysterectomy due to UL of 1.82 (95%CI 1.17; 2.82) among black women, after adjusting for variables such as age, body mass index (BMI), length of time since previous pregnancy, history of infertility, alcohol use, smoking, leisure-time physical activities, age of menarche, age of first pregnancy, use of oral contraceptives and marital status ²³23. Marshall LM, Spiegelman D, Barbieri RL, Goldman MB, Manson JE, Colditz GA et al. Variation in the incidence of uterine leiomyoma among premenopausal women by age and race. Obstet Gynecol 1997; 90 (6): 967-73. . Faerstein et al reported that black women had a nine times greater chance of presence of UL (OR: 9.4; 95%CI: 5.7; 15.7), after adjusting for age of menarche, use of oral contraceptives, smoking, body weight, arterial hypertension, diabetes mellitus, and history of pelvic inflammatory disease ²⁶26. Faerstein E, Szklo M, Rosenshein N. Risk factors for uterine leiomyoma: a practice-based case-control study. I. African-American heritage, reproductive history, body size, and smoking. Am J Epidemiol 2001; 153(1): 1-10. . Baird et al observed an odds ratio of 2.7, (95%CI: 2.3; 3.2) for black women, after adjusting for BMI and parity ⁴4. Day Baird D, Dunson DB, Hill MC, Cousins D, Schectman JM. High cumulative incidence of uterine leiomyoma in black and white women: ultrasound evidence. Am J Obstet Gynecol 2003; 188(1):100-7. .

With regard to socioeconomic variables, there are few studies on their associations with the occurrence of UL, thus hindering comparisons between the present study and the epidemiological literature. The great majority of etiological studies on UL analyze proximal factors associated with hormonal imbalance (estrogen and progesterone), not dealing with the social determinants (distal factors) of this causal chain. In this sense, variables such as level of education have been analyzed ³⁰30. Marshall LM, Spiegelman D, Goldman MB, Manson JE, Colditz GA, Barbieri RL et al. A prospective study of reproductive factors and oral contraceptive use in relation to the risk of uterine leiomyomata. Fertility Sterility 1998; 70(3): 432-9. ^{, 31}30. Marshall LM, Spiegelman D, Goldman MB, Manson JE, Colditz GA, Barbieri RL et al. A prospective study of reproductive factors and oral contraceptive use in relation to the risk of uterine leiomyomata. Fertility Sterility 1998; 70(3): 432-9. ^{, 34}34. Wise LA, Palmer JR, Spiegelman D, Harlow BL, Stewart EA, Adams-Campbell LL et al. Influence of body size and body fat distribution on risk of uterine leiomyomata in U.S. black women. Epidemiology 2005;16(3): 346-54. ^{, 39}39. Baird DD, Dunson DB, Hill MC, Cousins D, Schectman JM. Association of physical activity with development of uterine leiomyoma. Am J Epidemiol 2007; 165(2): 157-63. ^{, 42}42. Wise LA, Palmer JR, Harlow BL, Spiegelman D, Stewart EA, Adams-Campbell LL et al. Reproductive factors, hormonal contraception, and risk of uterine leiomyomata in African-American women: a prospective study. Am J Epidemiol 2004; 159(2): 113-23. as possible confounders of the remaining associations, thus not being the main focus of analysis.

Nonetheless, considering the few studies that approach the association between level of education and UL, some were found to lack such association ⁴4. Day Baird D, Dunson DB, Hill MC, Cousins D, Schectman JM. High cumulative incidence of uterine leiomyoma in black and white women: ultrasound evidence. Am J Obstet Gynecol 2003; 188(1):100-7. ^{, 40}40. Samadi AR, Lee NC, Flanders WD, Boring JR, Parris EB. Risk factors for self-reported uterine fibroids: A case-control study. Am J Public Health 1996; 86(6): 858-62. ^{, 55}55. Sato F, Miyake H, Nishi M, Mori M, Kudo R. Early normal menstrual cycle pattern and the development of uterine leiomyomas. J Womens Health Gender Based Med 2000; 9(3): 299-302. ^{, 56}56. Martin CL, Huber LRB, Thompson ME, Racine EF. Serum micronutrient concentrations and risk of uterine fibroids. J Womens Health 2011; 20(6): 915-21. and one study showed a direct association ²⁸28. Chiaffarino F, Parazzini F, La Vecchia C, Chatenoud L, Di Cintio E, Marsico S. Diet and uterine myomas. Obstet Gynecol 1999; 94(3): 395-8. . Two studies dealt with the influence of exposures occurring during the intrauterine life and childhood ⁵⁷57. D`Aloisio AA, Baird DD, DeRoo LA, Sandler DP. Association of intrauterine and early-life exposures with diagnosis of uterine leiomyomata by 35 years of age in the sister study. Environ Health Perspec 2010; 118(3): 375-81. <sup>, 58</sup>58. D`Aloisio AA, Baird DD, DeRoo LA, Sandler DP. Early-life exposures and early-onset uterine leiomyomata in black women in the sister study. Environ Health Perspec 2012; 120(3): 406-12. and found direct associations between tumors and parents' low level of education, food insecurity, and low household income during childhood among white women ⁵⁷57. D`Aloisio AA, Baird DD, DeRoo LA, Sandler DP. Association of intrauterine and early-life exposures with diagnosis of uterine leiomyomata by 35 years of age in the sister study. Environ Health Perspec 2010; 118(3): 375-81. , but not among black ones <sup>58</sup>58. D`Aloisio AA, Baird DD, DeRoo LA, Sandler DP. Early-life exposures and early-onset uterine leiomyomata in black women in the sister study. Environ Health Perspec 2012; 120(3): 406-12. .

There is much yet to be investigated in terms of how biological mechanisms are associated with socioeconomic and demographic characteristics, influencing health outcomes such as UL and including ways of determination apart from hormonal imbalance or health behavior. The present study showed indications that the frequency of UL is higher among black women and those with poorer socioeconomic conditions. Other epidemiological studies of a longitudinal analytical nature can better clarify the causal relations of interest, enabling action strategies related to this problem to be more effective and regulated by the search for greater equality in the sphere of women's health.

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