This population-based case-control study aims to verify the risk factors associated with preterm birth (PTB) in a maternity school. The cases were newborns with a gestational age greater than or equal to 22 weeks and less than 37 weeks (birth weight greater than or equal to 500 g), and controls were those born with gestational age equal to or greater than 37 weeks gestation. Data are recorded in the Live Birth Information System of 3,915 births at the Januário Cicco Maternity School in the year 2017. Pearson's chi-square test was used in conjunction with the adjusted residuals analysis and a hierarchical logistic regression analysis to verify the predictive variables of PTB. The variables were placed into a hierarchy and grouped into sociodemographic variables, reproductive history, and gestational and birth factors. A total of 976 cases and 2,377 controls were allocated for the analyzes, approximately (1:2.5). None of the maternal sociodemographic variables presented enough relation to prematurity to be inserted into the regression model. The model containing the variables of reproductive history shows that an obstetric history of up to two previous vaginal deliveries was related to PTB [X² = 24.450; p < 0.001, R² Cox and Snell = 0.007]. The model containing the variables of gestational factors, as multiple pregnancy, was the one that best explained prematurity and presented a determination power of 6.7% [X² = 232.8; p < 0.001, R² Cox and Snell = 0.067]. Multiple gestation, inadequate prenatal follow-up, anomalous presentations and obstetric history of up to two vaginal deliveries are risk factors for PTB.