Preterm delivery, defined as delivery occurring before 37 complete weeks of gestation, causes the majority of neonatal deaths unrelated to congenital anomalies and also accounts for more than one half of nursery costs. Furthermore, premature infants who survive often have significant morbidities including necrotizing enterocolitis, retinopathy of prematurity, intraventricular hemorrhage, chronic lung disease and developmental delay. Approximately one in 10 deliveries occurs preterm. Identifying and treating the underlying cause of preterm labor would potentially decrease perinatal morbidity and mortality. Unfortunately, the etiology in most cases of preterm labor is unknown. Some identified factors include anatomic abnormalities of the uterus and cervix, premature rupture of the membranes (PROM), placenta previa or abruption, trauma, excessive uterine enlargement, as in multiple gestation and hydramnios, and infection. The relationship between genitourinary infections and preterm labor will be discussed in this book.