Histologic chorioamnionitis and preterm delivery in different patient populations.

The placentas of 1843 deliveries were examined for the presence of histologic chorioamnionitis, which was classified as mild, moderate, or severe. Chorioamnionitis was present in 7.5% of patients who underwent cesarean before labor and in 18 and 32% of those delivering at term and preterm, respectively. Chorioamnionitis was severe in 74% of preterm but in only 15% of term deliveries. Premature rupture of membranes (PROM) was more frequent with preterm than with term delivery, with chorioamnionitis present in 42 and 15% of patients, respectively. Although chorioamnionitis was equally frequent in women with intact membranes delivering preterm and term, chorioamnionitis was severe in 63% of preterm and 14% of term deliveries (P less than .001). The frequency and severity of chorioamnionitis were related inversely to gestational age at preterm birth. Preterm delivery was more frequent in black than in white patients (19 versus 9%) and in indigent clinic versus private patients (13 versus 7.5%). However, there was no significant difference in frequency and severity of chorioamnionitis between black and white or between indigent clinic and private patients who delivered preterm. Among term births, chorioamnionitis was more often severe in black than in white patients. Chorioamnionitis in term deliveries was more frequent in clinic than in private patients; however, this was not true when only severe chorioamnionitis was considered. There were no differences in PROM between these patient populations. Thus, higher preterm birth rates in black and indigent clinic populations are not due to the more frequent occurrence of chorioamnionitis.