Despite extensive research, the etiology of most preterm births remains unknown. There are significant fetal consequences associated with preterm birth, which include necrotizing enterocolitis, fetal respiratory distress and intra-ventricular hemorrhage. Perinatal mortality is about 44%, 11% and 5% when deliveries occur between 25-28 weeks, 29-32 weeks and 33-34 weeks, respectively. While for many years, it was assumed that the cause of the high morbidity associated with prematurity was the birth of a neonate with a restricted adaptive capacity, it has also been suggested that part of the high perinatal morbidity was the consequence of adverse processes affecting the fetus in utero, rather than of prematurity per se. Intra-amniotic inflammation present in utero early in gestation may trigger the cascade of events leading to preterm birth (i.e. rupture of membranes, cervical ripening, uterine contractions) and provide an intrauterine milieu which is unfavorable or even harmful to the fetus.