Origin and levels of trypsin in amniotic fluid throughout pregnancy.

Trypsin is present in midtrimester amniotic fluid with a mean level of 350 +/- 260 ng/ml, but has virtually disappeared by term. The trypsin originates in fetal pancreas and it is suggested that its mode of entry into the gestation sac is by passage of meconium which ceases as a physiological event by 16-18 weeks. The finding could form the basis of an antenatal test for the presence of cystic fibrosis in the fetus.