Amniotic fluid volume in intra-amniotic inflammation with and without culture-proven amniotic fluid infection in preterm premature rupture of membranes

Objective: Previous studies reported that the clinical significance of intra-amniotic inflammation with a negative amniotic fluid (AF) culture is similar to that of intra-amniotic inflammation with microbiologically-proven AF infection. However, the magnitude of the fetal inflammatory response in these two conditions is different as gauged by umbilical cord C-reactive protein (CRP) concentrations. We undertook this study to determine if the frequency of oligohydramnios is different in these two conditions. Methods: The amniotic fluid index (AFI) was measured in 205 patients with preterm premature rupture of membranes (PROM) (<= 35 weeks). AF was cultured for aerobic and anaerobic bacteria and genital mycoplasmas. Intra-amniotic inflammation was defined as an elevated AF matrix metalloproteinase-8 (MMP-8) concentration (>23 ng/mL). Patients were divided into three groups according to the results of AF culture and the presence or absence of intra-amniotic inflammation: 1) without intra-amniotic inflammation and a negative culture (n=109); 2) with intra-amniotic inflammation and a negative culture (n=44); and 3) a positive culture (n=52). Results: Patients with a positive culture had a higher frequency of oligohydramnios and a lower median AFI than those with a negative culture but with intra-amniotic inflammation (P<0.01). However, there was no significant difference in the median AFI or in the frequency of oligohydramnios according to the presence or absence of intra-amniotic inflammation among patients with a negative culture (P>0.1). Conclusion: Oligohydramnios was more frequent in patients with culture-proven AF infection than in those with intra-amniotic inflammation and a negative AF culture.