Intrauterine infection, preterm labor, and cytokines.

and mortality worldwide. Spontaneous preterm labor, with intact or rupture of the chorioamniotic membranes, is responsible for two-thirds of all preterm births. The cost of preterm birth to society is estimated to be approximately $20 billion per year in the United States alone.1 Until recently, preterm labor was considered to result from extemporaneous activation of the components ofthe common pathway of parturition: myometrial contractility, cervical ripening, and/or decidual activation.2'3 Therefore, many investi gators believed that understanding the mechanisms responsible for normal parturition at term would lead to methods to treat and prevent preterm labor/delivery. This paradigm has not fulfilled its promise, as elucidation of the physiology of parturition has proven to be far more complex than anticipated4 17 and it is now apparent that preterm labor is not simply "labor before its time."4 Preterm parturition is now considered a syndrome caused by multiple pathologic processes able to activate the common terminal pathway of