A Rapid Amniotic Fluid Interleukin-6 Assessment for the Identification of Intra-Amniotic Inflammation in Women with Preterm Labor and Intact Membranes

Objectives: A multivariable predictive model has recently been developed with good accuracy to predict spontaneous preterm delivery within 7 days in women with preterm labor (PTL) and intact membranes. However, this model measures amniotic fluid (AF) interleukin (IL)-6 concentrations using the ELISA method, thereby limiting clinical implementation. The main objectives of this study were to validate the automated immunoassay as a quantitative method to measure AF IL-6 in women with PTL and to evaluate the diagnostic performance of AF IL-6 alone and as part of a multivariable predictive model to predict spontaneous delivery in 7 days with this automated method.

Study design: This is a retrospective observational study in women with PTL below 34 weeks who underwent amniocentesis to rule out microbial invasion of the amniotic cavity. Women with clinical signs of chorioamnionitis, cervical length measurement at admission >5th centile, maternal age <18 years, and no consent to perform amniocentesis for this indication were excluded. The local Institutional Review Boards approved the study (HCB/2019/0940). Analysis of AF IL-6 Concentrations: AF IL-6 concentrations were measured using an automated Cobas e602 electrochemiluminescence immunoanalyzer and Human IL-6 Quantikine ELISA kit.

Results: Of the entire study group (n = 100), 38 women spontaneously delivered within 7 days after admission. Both laboratory methods showed good agreement (intraclass correlation coefficient: 0.937 (95% confidence interval [CI] 0.908-0.957); p < 0.001). Diagnostic performance of AF IL-6 to predict spontaneous delivery within 7 days when it was included in the multivariable predictive model showed an area under the receiver operating characteristic curve of 0.894 (95% CI 0.799-0.955), sensitivity of 97%, specificity of 74%, positive predictive value of 73%, negative predictive value of 97%, positive likelihood ratio (LR) of 3.7, and negative LR of 0.045.

Conclusion: While both analytical methods were comparable for measuring AF IL-6 concentrations in women with PTL, the Cobas immunoanalyzer provided rapid diagnosis of intra-amniotic inflammation within minutes. The predictive model showed a good diagnostic performance to target women at high risk of spontaneous delivery within 7 days.