Reference values for gamma-glutamyl-transferase in amniotic fluid in normal pregnancies

Nonvisualization of the fetal gallbladder by ultrasound poses a diagnostic dilemma. The aim of the study was to establish reference values for the hepatobiliary enzyme gamma-glutamyl-transferase (GGT) in amniotic fluid in normal pregnancies, and to determine the maximal week of gestation in which reference values can be determined.

A cross-sectional design was used. The study group consisted of pregnant women at 16 gestational weeks or more referred to our ultrasound unit for amniocentesis. Amniotic fluid was assayed for levels of GGT and other hepatobiliary enzymes using the Integra 800 device. The 5th and 95th percentiles for each gestational week were calculated.

A total of 263 samples were analyzed. After conversion to log units, enzyme levels showed a good correlation with gestational week (Pearson). The mean values and the 5th and 95th percentiles were calculated for gestational weeks 16 to 22. Beyond 22 weeks, the number of examinations was insufficient for analysis. On multiple regression analysis, log values of alkaline phosphatase, maternal age, and gestational age independently affected log GGT values. Levels of alkaline phosphatase, aspartate aminotransferase, and alanine aminotransferase were too low, and their correlation with gestational week too poor for calculation of reference values.

GGT reference values in amniotic fluid in normal pregnancies were defined for gestational weeks 16 to 22. These data may be useful for differentiating isolated absence of fetal gallbladder from extrahepatic biliary atresia.