Defining preterm delivery - the epidemiology of clinical presentation

It is possible that preterm delivery is not a single entity but a cluster o f conditions with different aetiologies that ultimately result in the deliv ery of an infant before 37 completed weeks of gestation. Whereas some resea rchers have reported aetiological heterogeneity, others have found no diffe rences between subtypes or have disputed the desirability and utility of cl assifying preterm birth into subtypes. This study explores the relationship of maternal risk factors to type of preterm delivery in a cohort of over 7 000 black and white women delivering singleton infants at the University of California, San Francisco's Moffitt Hospital between 1980 and 1990. Althou gh the magnitude of the effect of individual risk factors differed between preterm delivery subtypes, the set of risk factors significantly associated with both categories of spontaneous preterm delivery was identical, while that associated with medically indicated preterm births was different. This study indicates that whereas the distinction between spontaneous preterm d eliveries and those that are medically indicated seems valid, distinguishin g between types of spontaneous preterm births may not lead to useful aetiol ogical inferences.