The risk of intra-amniotic infection, inflammation and histologic chorioamnionitis in term pregnant women with intact membranes and labor.

Objective: A previous study has demonstrated that term labor is associated with an increased risk of microbial invasion of the amniotic cavity, intra-amniotic inflammation and histologic chorioamnionitis. This study was performed to determine when the risk of intra-amniotic infection, inflammation and histologic chorioamnionitis begins to increase during the course of labor.
Study Design: Amniotic fluid (AF) was obtained from 926 term singleton pregnant women with intact membranes during cesarean section. AF was cultured for aerobic, anaerobic bacteria and genital mycoplasmas. An AF white blood cell (WBC) count was determined. Patients were divided into five groups according to the absence or presence of regular uterine contractions and the degree of cervical dilatation. Intra-amniotic inflammation was defined as an AF WBC ≥ 19/mm(3). Histologic chorioamnionitis was defined as the presence of acute inflammatory changes in the extra-placental membranes or the chorionic plate of the placenta, and funisitis was diagnosed in the presence of neutrophil infiltration into the umbilical vessel walls or Wharton's jelly.
Results: (1) The more advanced the cervical dilatation, the greater the risk of intra-amniotic infection and/or inflammation and histologic chorioamnionitis; (2) The risk of intra-amniotic infection and/or inflammation increased after the cervix began to dilate (7.8% in group 1 [without regular uterine contractions] vs. 18.3% in group 2 [regular uterine contractions and cervical dilation ≤1 cm], p < 0.01); (3) however, histologic chorioamnionitis was significantly more common in women in group 3 than in group 2 (4.2% in group 2 [regular uterine contractions and cervical dilatation ≤1 cm] vs. 23.1% in group 3 [regular uterine contractions and a cervical dilatation of 2-3 cm], p < 0.05).
Conclusions: The risk of intra-amniotic infection and/or inflammation increases after the cervix begins to dilate and that of histologic chorioamnionitis increases after the cervix dilates 2 cm in term pregnant women with regular uterine contractions with intact membranes.
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