The diagnosis and treatment of preterm labor is currently based on an inadequate literature. Not only is there a paucity of welldesigned and adequately powered clinical trials, but there is incomplete understanding of the sequence and timing of events that precede clinical evidence of preterm labor. To date, there is no single test or sequence of assessment measures to accurately predict preterm birth. Prevention of preterm birth has primarily focused on the treatment of the woman with symptomatic preterm labor. Treatment has been directed toward the inhibition of contractions. This approach has not decreased the incidence of preterm birth but can delay delivery long enough to allow administration of antenatal steroids and to transfer the mother and the fetus to an appropriate hospital, two interventions that have consistently been shown to reduce the rates of perinatal mortality and morbidity. Preterm birth has historically not been emphasized in prenatal care, in the belief that the majority of preterm births are due to social rather than medical or obstetric causes or are the appropriate result of pathological processes that would benefit the mother or the infant, or both. Because preterm labor or premature rupture of membranes may occur in response to conditions that threaten fetal or maternal well-being, whether preterm birth is appropriately preventable is a topic that regularly influences clinical decision making. The ultimate goal of treatment for preterm labor is to eliminate or reduce