Association between third-trimester aspartate aminotransferase-to-platelet ratio index and bile acid-defined disease severity in intrahepatic cholestasis of pregnancy

To evaluate whether the third-trimester Aspartate Aminotransferase-to-Platelet Ratio Index (APRI) is independently associated with bile acid-defined disease severity in women with intrahepatic cholestasis of pregnancy (ICP). This retrospective cohort study included 80 singleton pregnancies complicated by ICP. Disease severity was classified according to fasting serum total bile acid concentrations as mild (10–39 µmol/L), moderate (40–99 µmol/L), or severe (≥ 100 µmol/L). Third-trimester APRI values were compared across severity groups using the Kruskal–Wallis test. Correlation between APRI and fasting serum total bile acid concentrations was assessed using Spearman’s rank correlation. Multivariable ordinal logistic regression was performed to determine whether APRI was independently associated with disease severity after adjustment for maternal age, gravidity, and parity. The median third-trimester APRI was 0.37 (interquartile range [IQR], 0.19–0.65), and the median fasting serum total bile acid concentration was 41 µmol/L (IQR, 18.0–86.5). Median APRI values increased numerically across mild, moderate, and severe ICP but did not differ significantly between severity groups ( p = 0.112; η²_H = 0.031). APRI demonstrated a weak but statistically significant positive correlation with fasting serum total bile acid concentrations (Spearman’s r = 0.262, p = 0.019). In multivariable ordinal logistic regression analysis, third-trimester APRI was not independently associated with increasing ICP severity (adjusted OR per 0.1-unit increase = 1.011, 95% CI: 0.969–1.054, p = 0.612). However, a sensitivity analysis excluding one extreme APRI observation revealed a significant adjusted association with ICP severity (adjusted OR per 0.1-unit increase = 1.080, 95% CI 1.006–1.158; p = 0.033), indicating that the primary regression finding was sensitive to this observation. Third-trimester APRI demonstrated a weak positive correlation with fasting serum total bile acid concentrations but was not independently associated with bile acid-defined ICP severity in the primary analysis. The adjusted association was sensitive to a single extreme observation, and the overall discriminatory performance of APRI was limited. These findings do not support its use as a stand-alone marker for ICP severity stratification.