Immunoreactive trypsin and the prenatal diagnosis of cystic fibrosis.

Immunoreactive trypsin (IRT) was measured by radioimmunoassay in a series of amniotic fluids obtained at between 15 and 19 weeks from pregnancies with a 1-in-4 risk of fetal cystic fibrosis. IRT concentrations were significantly depressed in nine affected pregnancies, but the degree of overlap with the normal range was too great for this to be useful in early prenatal diagnosis. Furthermore, in one fetus, presumed to have cystic fibrosis, the fetal plasma IRT concentration was within the normal range.