Histologic Chorioamnionitis is More Common after Spontaneous Labor than after Induced Labor at Term

ObjectiveInflammation of the chorioamniotic membranes (histologic chorioamnionitis) is a risk factor for adverse neonatal outcome. Labor has many common features with inflammatory processes; therefore, an important question is whether the frequency of histologic chorioamnionitis in spontaneous labor at term is higher than that of women in labor after induction. This study was conducted to address this question.Study designThe frequency of histologic chorioamnionitis was compared between patients who delivered after the spontaneous onset of labor versus those who delivered after induction of labor at term in singleton gestations (≥37 weeks). Patients in whom uterotonic agents were used during the latent phase of labor were excluded.Results(1) The overall frequency of histologic chorioamnionitis was 20.2% (107/531); (2) histologic chorioamnionitis was significantly more frequent in women who delivered after the spontaneous onset of labor than in those who underwent induction of labor (24.3% [81/333] versus 13.1% [26/198], p < 0.005). This difference remained significant after adjusting for parity, gestational age at delivery, total duration of labor, the interval from rupture of membranes to delivery and the mode of delivery.ConclusionHistologic chorioamnionitis is more common in women who delivered after the spontaneous onset of labor than in those who underwent induction of labor at term.