Amniotic fluid beta-endorphin levels and labor.

To define the relationship between amniotic fluid concentrations of beta-endorphin immunoreactivity and onset of parturition, we measured this opioid in samples obtained during cesarean section at term. A total of 27 women were studied, 14 without labor and 13 in early labor. Mean (+/- SE) amniotic fluid beta-endorphin levels were significantly lower in patients in labor than in those not in labor (3.2 +/- 0.05 versus 8.4 +/- 1.0 fmol/mL). The mean beta-endorphin level (21.1 +/- 4.2 fmol/mL) in other amniotic fluid samples obtained during the second trimester of pregnancy was significantly higher than mean values at term. These differences in amniotic fluid beta-endorphin levels may support the theory of an opioid mechanism involved in parturition.