Preterm labor is a common obstetric complication, and prematurity is a major cause of perinatal death and long-term handicap. Despite this, the incidence of preterm labor has not changed for many years. Neonatology has advanced, and the surival of babies has improved, but handicap continues to occur in babies born at earlier gestations. The reason for – our inability to manage or prevent preterm labor adequately is simply the lack of knowledge of its causes. However, we are now beginning to understand the possible mechanisms of preterm labor.