Presence of immunoassayable β-endorphin in human amniotic fluid: Elevation in cases of fetal distress

Immunoassayable β-endorphin is present in samples of amniotic fluid obtained in the last two weeks of pregnancy. Average concentration is approximately 300 pg. per milliliter. In all cases of suspected or recognized fetal distress, striking elevations of the β-endorphin concentrations (twofold to 20-fold) were observed. The degree of elevation correlated with the degree of fetal distress.