Abstract
Objectives: Microbial invasion of the amniotic cavity (MIAC) can affect outcomes following rescue cerclage. We carried out a study to compare the diagnostic performance of the Gram stain and glucose tests for detecting subclinical MIAC.
Methods: We used individual-level data from published studies on Gram stain, glucose, and amniotic fluid culture among women with preterm labour. We calculated the sensitivity, specificity, area under the curve (AUC) and other indices, with amniotic fluid culture results used as the gold standard. The probability of infection using both tests as predictors was also estimated using logistic regression.
Results: The rate of culture-confirmed MIAC was 11.8% (34 of 288 women). The Gram stain test yielded a sensitivity of 65% (95% CI 46% to 78%) and a specificity of 99% (95% CI 98% to 100%). A positive Gram stain or glucose test had a sensitivity of 88% (95% CI 72% to 96%) and a specificity of 87% (95% CI 82% to 90%), while a positive Gram stain and a positive glucose test had a sensitivity of 62% (95% CI 44% to 77%) and a specificity of 100% (95% CI 98% to 100%). The AUC for the tests were Gram stain 0.82 (95% CI 0.74 to 0.90), glucose 0.86 (95% CI 0.80 to 0.93), and combined Gram stain and glucose 0.92 (95% CI 0.86 to 0.98). Using the tests, singly or in combination, provided greater clinically important calibration, risk-stratification, and classification accuracy than using no tests.
Conclusion: Amniotic fluid Gram stain and/or glucose testing provides substantially improved performance for the diagnosis of subclinical MIAC compared with no testing.