Serum bile acid concentrations during pregnancy and their relationship to obstetric cholestasis.

We have prospectively studied changes in serum postprandial cholylglycine (CG) concentration during 297 pregnancies. We found an increase in CG concentration from 0.3 mumol/L at 15 weeks' pregnancy to 0.6 mumol/L at 40 weeks' pregnancy. Although this increase was statistically significant (p less than 0.005), median concentrations of CG remained well within the normal range (0-1.5 mumol/L). However, 10% of the group showed markedly elevated serum CG concentrations at 30 weeks' pregnancy, and the CG level in this group continued to rise during the third trimester. Pruritus was significantly more common in the group with elevated CG concentrations (48%) than in the group with normal CG levels (20%) (p less than 0.005). Serum CG was a much more sensitive predictor of pruritus during pregnancy than other biochemical liver tests. Elevated CG levels were found more commonly in Mediterranean and Asian patients than patients of other ethnic origins (p less than 0.025). No statistically significant associations were found between elevated CG concentrations and maternal age, number of previous pregnancies, pruritus during previous pregnancies, contraceptive-induced cholestasis, and fetal maturity. We conclude that obstetric cholestasis is probably much more common than previously suspected and that consideration should be given to the measurement of serum bile acids in all pregnant individuals with unexplained pruritus.