Diagnostic Accuracy of Fetal Thymus Transverse Diameter on Ultrasound for Prediction of Chorioamnionitis in Preterm Prelabor Rupture Of Membranes (PPROM): Histopathology as the Gold Standard

Abstract

Objectives: To determine the diagnostic accuracy of fetal thymus transverse diameter measured by ultrasound for predicting chorioamnionitis in women with preterm prelabor rupture of membranes (PPROM), using histopathology as the gold standard.

Study design: Cross-sectional validation study.

Place and duration of study: Department of Obstetrics and Gynecology, Sir Ganga Ram Hospital, Lahore. From June-2024 to December-2024.

Methodology: A total of 105 women aged 18 to 40 years, gestational age ≥22 and <37 weeks, with singleton pregnancy, and diagnosed with PPROM were enrolled.  Ultrasound was performed at the time of admission, and the fetal thymus was visualized in the transverse section of the fetal thorax at the three-vessel view. A small fetal thymus was considered when it was below the 5th percentile for gestational age. Placental and membrane tissues were examined histopathologically for chorioamnionitis after delivery. Diagnostic accuracy parameters, including sensitivity, specificity, and predictive values, were calculated.

Results: Histopathology diagnosed chorioamnionitis in 45 (42.86%), while a small fetal thymus was detected by ultrasound in 46 (43.81%) of women. There were 39 true positive, 7 false positive, 6 false negative, and 53 true negative cases. This assessment tool showed a sensitivity of 86.67%, specificity of 88.33%, positive predictive value of 84.78%, negative predictive value of 89.83%, and overall diagnostic accuracy of 87.62%.

Conclusion: Ultrasound assessment of fetal thymus transverse diameter demonstrated a good diagnostic accuracy for predicting chorioamnionitis in women with PPROM and therefore may serve as a useful non-invasive antenatal marker.