Preterm histologic chorioamnionitis: impact on cord gas and pH values and neonatal outcome

The purpose of this study was to further delineate the impact of preterm chorioamnionitis on a spectrum of neonatal outcomes using a large tertiary hospital population.

The perinatal/neonatal and placental pathology databases of St. Joseph's Health Care, London, Ontario, Canada, were used to obtain the umbilical cord gas and pH values, incidence of adverse neonatal outcomes, patient demographics, and placental pathology reports for all preterm (25 to 34 weeks of gestation), singleton, liveborn infants with no major anomalies who were delivered with spontaneous onset of labor or for suspected chorioamnionitis between November 1, 1995, and October 31, 2003. Patient groupings on the basis of placental inflammation and clinical chorioamnionitis were studied by a comparison of mean values and incidences for those neonatal outcomes that were available from the database with the use of linear and logistic regression analysis and controlling for potentially confounding variables.

There were 660 infants who met the inclusion criteria and had placental pathology available of whom 368 (56%) had no placental inflammation, 114 (17%) had placental chorioamnionitis, and 178 (27%) had placental funisitis. Umbilical cord partial pressure oxygen and base excess values were generally higher in the placental inflammation/clinical chorioamnionitis groups, in keeping with enhanced oxygen delivery and an overall decrease in the metabolic contribution to acidosis attributed to altered lactate metabolism in these infants. After adjusting for confounders (primarily differences in gestational age), the incidence of respiratory distress syndrome was significantly decreased in the placental inflammation/clinical chorioamnionitis groups, in keeping with cytokine-induced synthesis of surfactant proteins in these infants. Although the incidence of bronchopulmonary dysplasia, intraventricular hemorrhage, and periventricular leukomalacia was generally unchanged among the groups studied, that for intraventricular hemorrhage and periventricular leukomalacia was lowest in the placental inflammation/no clinical chorioamnionitis patients and highest in the placental inflammation/clinical chorioamnionitis patients, suggesting a differential effect of clinical chorioamnionitis for these outcomes.

Overall, infants born preterm with intrauterine infection were better oxygenated and showed less metabolic acidosis at birth and had incidences of respiratory distress syndrome and intraventricular hemorrhage, which were variably lower. Although there are likely threshold levels of inflammatory cytokines that do give rise to adverse outcome, a minimal level of cytokines may also be beneficial for the transition at birth from intrauterine to extrauterine existence when preterm pending the circumstances (ie, exposure to antenatal steroids) and emphasizing the complex relationship among preterm birth, infection, and adverse neonatal outcome.