Histological chorioamnionitis at term: Clinical correlates and performance of the Triple I criteria

Histological chorioamnionitis frequently occurs at term in the absence of clinical signs of intrauterine inflammation. The diagnostic accuracy of suspected intraamniotic infection or inflammation (Triple I) criteria in term pregnancies remains unclear.

To evaluate the diagnostic performance of suspected Triple I criteria for identifying histological chorioamnionitis at term.

This retrospective case-control study included singleton term pregnancies (≥37 weeks) delivered between 2021 and 2024 at a tertiary referral center. Cases were defined by histological chorioamnionitis, and controls were randomly selected (1:1 ratio) among placentas without histological evidence of inflammation during the same study period. Diagnostic performance of suspected Triple I within the last 24 h before delivery was assessed using sensitivity, specificity, predictive values, likelihood ratios, and ROC curve analysis.

Among 438 women (219 cases, 219 controls), suspected Triple I was present in 27.9% of cases. Triple I showed low sensitivity and high specificity (96.8%), with a positive likelihood ratio of 8.71 and an AUC of 0.623 (95% CI 0.571-0.675, p < 0.001). A positive result increased the post-test probability from 15% to approximately 61%, whereas a negative result only slightly reduced it. At multivariable analysis, gestational age at delivery (aOR 1.63, 95% CI 1.22-2.19), and fetal tachycardia (aOR 4.08, 95% CI 1.76-9.49) were independently associated with histological chorioamnionitis.

At term, suspected Triple I criteria have limited sensitivity but high specificity for histological chorioamnionitis, supporting their use as a rule-in rather than rule-out tool. These findings highlight the need for improved diagnostic strategies integrating clinical parameters with biomarkers.