Background: Chorioamnionitis is the association of microorganisms infection in fetal membrane, placental membrane and amniotic fluid. About 2 to 4% of chorioamnionitis occurs in full-term deliveries, but higher than this prevalence in preterm birth. Objectives: The objective of this study was to detect the most dominant bacteria of chorioamnionitis and evaluate correlation of the presence of microorganisms infection in placental membrane, fetal membrane and amniotic fluids in women with preterm birth