Clinical Chorioamnionitis at Term: New Insights into the Etiology, Microbiology, and the Fetal, Maternal and Amniotic Cavity Inflammatory Responses

Abstract

Clinical chorioamnionitis is the most common infection related diagnosis made in labor and delivery units worldwide. It is traditionally believed to be due to microbial invasion of the amniotic cavity, which elicits a maternal inflammatory response characterized by maternal fever, uterine tenderness, maternal tachycardia and leukocytosis. The condition is often associated with fetal tachycardia and a foul smelling amniotic fluid. Recent studies in which amniocentesis has been used to characterize the microbiologic state of the amniotic cavity and the inflammatory response show that only 60% of patients with the diagnosis of clinical chorioamnionitis have proven infection using culture or molecular microbiologic techniques. The remainder of the patients have intra-amniotic inflammation without demonstrable microorganisms or a maternal systemic inflammatory response (fever) in the absence of intra-amniotic inflammation. The latter cases often represent a systemic inflammatory response after epidural anesthesia/analgesia has been administered. The most common microorganisms are Ureaplasma species and Gardnerella vaginalis. In the presence of ruptured membranes, the frequency of infection is 70%, which is substantially higher than patients who have intact membranes (25%). The amniotic fluid inflammatory response is characterized by an infiltration of neutrophils and monocytes. Both cell types are activated in the presence of infection and can produce inflammatory cytokines. The white blood cells in the amniotic fluid can be of fetal or maternal origin. The maternal inflammatory response is characterized by an elevation in the concentration of pyrogenic cytokines. The cytokine plasma concentrations in the fetal circulation are elevated even if there is no evidence of an intra-amniotic inflammatory response suggesting that maternal plasma cytokines may cross the placental barrier and induce a mild fetal inflammatory response. Placental pathology is of limited value in the diagnosis of proven intra-amniotic infection. The clinical criteria traditionally used in clinical medicine have accuracy around 50% and therefore, they cannot distinguish between patients with a proven intra-amniotic infection and those with intra-amniotic inflammation alone. Analysis of amniotic fluid with a bedside test for MMP-8 can allow the rapid identification of the patient at risk for infection and may decrease the need for antibiotic administration to neonates. An important consideration is whether antibiotics effective against Ureaplasma species should be administered to patients with clinical chorioamnionitis, given that these genital mycoplasmas are the most common organisms found in the amniotic fluid. The emergent picture is that clinical chorioamnionitis is a heterogeneous syndrome, which requires further study to optimize maternal and neonatal outcomes.

Keywords: Intra-amniotic infection; MMP-8; amniotic fluid; antibiotics; biomarkers; cytokines; fetal tachycardia; maternal fever; maternal morbidity; monocytes; neonatal morbidity; neutrophils; rapid diagnosis; treatment.

Figure 1.

Prevalence of microbial-associated intra-amniotic inflammation and intra-amniotic inflammation without detectable microorganisms in patients with clinical signs of chorioamnionitis at term according to the status of the membranes at the time of amniocentesis (intact vs. ruptured). Microbial-associated intra-amniotic inflammation was diagnosed in 70% (21/30) of the cases with rupture of membranes, and in 25% (4/16) of patients with intact membranes.

Figure 2.

Histological examination of amniotic fluid neutrophils and monocytes in women with clinical chorioamnionitis. A) Hematoxylin & Eosin staining shows the typical morphology of neutrophils (N, green arrow) and monocytes (M, red arrow) in the amniotic fluid of women with clinical chorioamnionitis. Magnification 400X. Scale bars: 50μm. B) Immunofluorescence of neutrophils and monocytes in the amniotic fluid of women with clinical chorioamnionitis. Neutrophils (CD15+ cells) are green, monocytes (CD14+ cells) are red, and nuclei are blue (DAPI). Magnification 400X.

Figure 3.. DNA fingerprinting of amniotic fluid neutrophils.

DNA fingerprinting of purified amniotic fluid neutrophils of fetal (A), maternal (B) or mixed (C) origin, the fetus (umbilical cord), and the mother (buffy coat from peripheral blood) is shown in electropherograms. Each electropherogram contains 16 genetic sites: D3S1358, TH01, D21S11, D18S51, Penta_E, D5S818, D13S317, D7S820, D16S539, CSF1PO, Penta_D, X- and Y-specific amalogenin genes, vWA, D8S1179, TPOX, and FGA. Each electropherogram was separated into three sections: blue, green, and black. Each color indicates the dye used for the PCR multiplex: blue represents the genes amplified using fluorescein (FL dye), green represents the genes amplified using 6-carboxy-4′,5′-dichloro-2′,7′-dimethoxyfluorescein (JOE dye), and black represents the genes amplified using tetramethylrhodamine (TMR dye). Each genetic site has STR alleles, which is represented by peaks. The number next to/above each STR allele (peak) is the number of repeats for each STR allele.