Purpose: The aim of our study was to evaluate the oxidative stress (OS) in pregnant women with intrahepatic cholestasis of pregnancy (ICP) by evaluating thiol/disulphide homeostasis using an alternative technique.Methods: A total of 57 pregnant women with ICP were compared with 50 gestational age and body mass index matched controls. A recently defined method was used for the measurement of plasma native-total thiol and disulphide levels. The independent two-sample t test, Mann-Whitney-U test, Chi-square test, binary logistic regression with backward elimination and receiver operating characteristic (ROC) curve was performed for statistical analyses.Results: Pregnant women with ICP (n=57) versus controls (n=50) had significantly lower serum levels of native thiol (233.847.4mol/L vs. 308.5 +/- 51.7mol/L, p<.001), total thiol (258.4 +/- 46.5mol/L vs. 328.0 +/- 52.0mol/L, p<.001) and higher levels of disulphide (12.3 +/- 3.6mol/L vs. 9.7 +/- 3.4mol/L, p<.001). Binary logistic regression showed that the most important variables related to ICP were native thiol and total thiol. According to the ROC curve, the optimal cut-off level for native thiol was 280.0mol/L (sensitivity: 86%, specificity: 84.2%, area under the curve (AUC):0.896, 95% CI: 0.831-0.962, p<.001), and the optimal cut-off level for total thiol was 300.0mol/L (sensitivity: 86%, specificity: 80.7%, AUC: 0.883, 95% CI: 0.815-0.951, p<.001).Conclusions: To our knowledge, this is the first study in the literature exploring thiol/disulphide balance in ICP. We found that thiol/disulphide balance indicate OS in pregnant woman with ICP.