Lack of relationship between histologic chorioamnionitis and duration of the latency period in preterm rupture of membranes

It is often believed that the frequency of clinical chorioamnionitis in preterm premature rupture of membranes (PROM) increases with the duration of the interval between membrane rupture and delivery. We tested the hypothesis that the prevalence of histologic evidence of intrauterine infection increases proportionally to the duration of the latency period. A total of 191 consecutive placentas of singleton, nonanomalous, liveborn infants delivered at <32 weeks' gestation with PROM were examined prospectively. Demographic, obstetric, histopathologic, and neonatal information was obtained. Histopathologic evidence of acute inflammation in choriodecidua, amnion, umbilical cord, and chorionic plate was recorded and scored. The prevalence and severity of pathological evidence of intrauterine infection was correlated with the interval between membrane rupture and delivery. Maternal and neonatal outcomes were assessed in six groups defined by different intervals between membrane rupture and delivery. Statistical analysis utilized regression, Fisher's exact test, Chi-square, and one-way analysis of variance after log transformation where applicable. P < 0.05 was considered significant. No correlation was observed between total score of placental acute inflammation and the interval membrane rupture-to-delivery (r = 0.068, 95% confidence interval −0.075, 0.211; P = 0.35). There was no evidence that the rate of maternal (P = 0.4) or neonatal (P = 0.15) infectious morbidity, or the total score of acute placental inflammation (P = 0.13), acute amnionitis (P = 0.35), choriodeciduitis (P = 0.46), chorionic plate inflammation (P = 0.38), or umbilical and chorionic vasculitis (P = 0.06) increase with the prolongation of the PROM-to-delivery interval. This study had an 85% power to detect the lack of association that was actually observed. The rate of histologic evidence of chorioamnionitis in preterm PROM does not increase with the duration of the PROM-to-delivery interval. J. Matern.–Fetal. Med. 7:238–242, 1998. © 1998 Wiley-Liss, Inc.