There are several strands of evidence to suggest that even
in non-syndromic BA, the onset takes place early in gestation.
Antenatal ultrasonography allows detection of those
forms of BA that show cystic changes [19]. In a series of 10
infants detected antenatally, most were non-syndromic
and the first abnormal scans were observed at about 20
weeks of gestation [20]. In one study on serial digestive
enzyme sampling in amniotic fluid, gamma-glutamyl
transpeptidase (gamma-GTs) levels were found significantly
low as early as 18 weeks of gestation in infants born
with non-syndromic BA, providing strong evidence of biliary
obstruction at this term of gestation [21].