Statistical analysis
Clinical data, gynecological, laboratory and demographic variables of each participant were collected from their medical records. Independent variables associated to risk factors were: age, educational attainment, skin color, marital status, income, age at onset of sexual intercourse, number and previous abortion history. Data were analyzed by SPSS Version 12.0. The Chi-square and Poisson regression was also performed. Significant differences were considered when P values were lower than 0.05.