Trimester-Specific Diagnostic Accuracy of Amniotic Fluid α-Fetoprotein for Detecting Preterm Premature Rupture of Membranes Versus AmniSure

Abstract

Background: Preterm premature rupture of membranes (PPROM) is a critical obstetric complication that accounts for 3–10% of pregnancies and a substantial proportion of preterm births, with considerable maternal and neonatal morbidity. Early and precise diagnosis remains challenging because of limitations in current clinical tests, increasing the need for reliable biochemical markers. Materials and Methods: In this cross-sectional study, 177 pregnant women with clinical suspicion of PPROM before 37 weeks of gestation were enrolled and classified by trimester. Amniotic fluid alpha-fetoprotein (AFP), AmniSure, and Fern tests were performed on vaginal fluid samples. Sensitivity, specificity, and receiver operating characteristic (ROC) curve analyses were used to determine diagnostic performance, and optimal AFP thresholds were established for each trimester. Results: AFP distinguished PPROM from non-PPROM cases in all trimesters, with area under the ROC curve values exceeding 0.92 and reaching 0.97 in the third trimester. Trimester-specific AFP cutoffs maximized sensitivity (80.5-97.1%) and specificity (83.3–100%). The Fern test showed lower sensitivity and more discrepancies, particularly in early gestation, while the overall agreement between AmniSure and Fern testing was strong (κ=0.85). Conclusion: Vaginal fluid AFP measurement may be a practical and accurate diagnostic adjunct for PPROM across gestational ages, particularly when trimester-specific cutoffs are applied. AFP testing may be useful where access to proprietary assays is limited, but external validation is required before routine replacement of established diagnostic methods.