Histologic chorioamnionitis in pregnancies of various gestational ages. II: Implications in preterm labor.

A retrospective review of placental materials (membranes, chorionic plate, umbilical cord) derived from preterm birth is reported. All those studied had intact membranes on admission and did not have spontaneous rupture. Those with preterm labor unresponsive to tocolysis, including those with brief and more prolonged labors, were compared with those delivered preterm because of maternal or fetal indications without labor. Those with labor had inflammatory changes in all three sites of greater frequency than those without labor. Those with longer labors had significantly higher rates of inflammation than those without labor. In this population, removing the influence of spontaneous rupture and labor over 6 hours long greatly diminished the likelihood of inferring that inflammation of the choriamniotic environment is a cause of preterm labor unresponsive to tocolysis.