Serum Fatty Acid-Binding Protein 4: A Potential Diagnostic Marker Linking Lipid Metabolism and Inflammation in Intrahepatic Cholestasis of Pregnancy

Objective: This study aimed to investigate maternal serum fatty acid-binding protein 4 (FABP4) levels in pregnancies complicated by intrahepatic cholestasis of pregnancy (ICP) and to evaluate its diagnostic and prognostic utility for maternal and neonatal outcomes. Methods: This prospective case–control study included 44 women diagnosed with ICP and 44 gestational age-matched healthy pregnant controls between 24 and 41 weeks of gestation. Serum FABP4 concentrations were measured using a quantitative sandwich enzyme-linked immunosorbent assay (ELISA). Demographic, biochemical, and perinatal data were collected prospectively. Group comparisons were performed using the t-test or Mann–Whitney U test, correlations by Pearson or Spearman tests, and diagnostic performance by receiver operating characteristic (ROC) curve analysis. Results: Maternal serum FABP4 levels between 25 and 39 weeks of gestation were significantly higher in the ICP group than in the control group (median 3.60 [Q1–Q3: 3.25–4.20] vs. 2.40 [Q1–Q3: 2.00–2.95] ng/mL; p < 0.001). ROC analysis revealed excellent diagnostic accuracy for ICP (AUC = 0.899; 95% CI: 0.816–0.953; p < 0.001) with an optimal cut-off value of >3.0 ng/mL, yielding 90% sensitivity and 84% specificity. FABP4 correlated inversely with gestational age at delivery in the total cohort (r = −0.430, p < 0.001) but not within the ICP subgroup. In predicting composite neonatal outcomes, FABP4 showed moderate performance (AUC = 0.634, 95% CI: 0.525–0.734, p = 0.032) and limited predictive ability within the ICP group (AUC = 0.535, p = 0.685). Conclusions: Maternal FABP4 levels are significantly elevated in ICP and show high diagnostic accuracy for ICP but have limited prognostic value for neonatal outcomes. FABP4 may represent a novel biomarker reflecting the metabolic–inflammatory interplay underlying the pathophysiology of intrahepatic cholestasis of pregnancy.