OBJECTIVE Increased maternal serum bile acids are implicated in intrahepatic cholestasis of pregnancy. Individual bile acid profiles and their relationship with disease progression, however, remain unknown. The purpose of this prospective study was to determine the temporal changes in bile acids in normal pregnancy and in pregnancies complicated with intrahepatic cholestasis of pregnancy and pruritus gravidarum. METHODS A validated method for the evaluation of 15 bile acids (conjugated and unconjugated) in a single serum sample was developed using high-performance liquid chromatography/mass spectrometry (HPLC-MS) with an electrospray interface. Bile acid concentrations were assessed in samples (16 weeks of gestation to 4 weeks postpartum) from women with, or who later developed, intrahepatic cholestasis of pregnancy (n=63) and were compared with those from normal pregnant women (n=26) and from women with pruritus gravidarum (n=43). RESULTS Intrahepatic cholestasis of pregnancy was associated with a predominant increase in cholic acid conjugated with taurine and glycine, from 24 weeks of pregnancy. Ursodeoxycholic acid (UDCA) treatment (> or =21 days, n=15) significantly reduced serum taurocholic and taurodeoxycholic acid concentrations (P<0.01). Bile acid profiles were similar in normal pregnancy and pregnancy associated with pruritus gravidarum. CONCLUSIONS The bile acid profiles and effects of treatment by UDCA implicate a role for taurine-conjugated bile acids in the syndrome of intrahepatic cholestasis of pregnancy. [corrected] With regard to individual bile acid profiles, pruritus gravidarum is a disorder quite distinct from intrahepatic cholestasis of pregnancy.