Reference Range for Amniotic Fluid Bile Acids and Bilirubin in Uncomplicated Pregnancies

The objectives of the study were to establish reference values for bile acids and bilirubin levels in amniotic fluid and to assess their correlation to amniotic fluid digestive enzymes in normal pregnancies as a foundation for future diagnostic studies.

A prospective cross-sectional study was conducted.

Pregnant women with singleton pregnancies at 17-23 weeks undergoing amniocentesis for standard indications were selected for the study.

A single tertiary care center was chosen for the study.

Amniotic fluid levels of bile acids, total and direct bilirubin, aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, lactate dehydrogenase, and γ-glutamyl transferase (GGT) were measured. Gestational age-specific reference ranges were established.

A total of 133 women were recruited. The most common indication for amniocentesis was advanced maternal age. The 5th, 50th, and 95th percentiles of bile acids for the entire cohort were 1.3, 7.2, and 30.8 µm, respectively. There was no significant change in bile acid levels throughout gestational weeks. Mean, standard deviation, and median values for all hepatobiliary enzymes were calculated. On regression analysis a significant positive correlation between bile acids and GGT was found.

Absence of pathological cases for comparison and relatively small sample size at 22-23 weeks was considered a limitation.

Reference values for amniotic fluid bile acids and bilirubin at 17-23 weeks in normal pregnancies were established. The significant correlation between bile acids and GGT, combined with the direct biological relevance of bile acids in biliary pathology, suggests potential utility as complementary or alternative biomarkers in pregnancies complicated with non-visualization of the fetal gallbladder.