The inflammatory milieu of amniotic fluid in acute-chorioamnionitis decreases with increasing gestational age.

INTRODUCTION: The inflammatory milieu decreases in the placenta and amniotic fluid (AF) with gestational age (GA). However, there is no information about whether the inflammatory milieu of AF in the setting of the same placental inflammatory condition decreases with GA. We hypothesized that the inflammatory milieu of AF in acute chorioamnionitis would decrease with increasing GA.

METHODS: The inflammatory milieu of AF was examined in 617 singleton preterm pregnancies (<36 weeks) delivered within 5 days of amniocentesis. Study population was divided into GA at delivery ≤30 weeks (n = 148), 30-34 weeks (n = 226), and 34-36 weeks (n = 226). Acute-chorioamnionitis was classified according to the severity (i.e., mild, total grade 1; moderate, total grade 2; and severe, total grade 3-6) or involved compartment (i.e., chorionic plate, amnion and chorio-decidua). The inflammatory milieu of AF was determined by matrix metalloproteinase-8 (MMP-8) concentration.

RESULTS: 1) AF MMP-8 concentrations decreased in patients with acute-chorioamnionitis (P < 0.001), but not inflammation-free placenta, with increasing GA; 2) AF MMP-8 concentrations were less intense at higher GA in patients with moderate and severe (each-for P < 0.005), but not mild, acute-chorioamnionitis; 3) AF MMP-8 concentrations decreased in the context of the same involved compartment (i.e., chorionic plate inflammation, amnionitis, or chorio-deciduitis) of acute-chorioamnionitis (each-for P < 0.001) with increasing GA; 4) Moreover, there was a significant inverse relationship between GA and AF MMP-8 concentrations in patients with acute-chorioamnionitis (r = -0.453, P < 0.0000001), but not inflammation-free placenta (r = -0.071, P = 0.170).

DISCUSSION: AF MMP-8 concentrations in acute-chorioamnionitis distinctly decrease throughout preterm-gestation. This finding suggests that the inflammatory milieu of AF decrease in acute-chorioamnionitis with GA.