Quantitative relationships between pain intensities during labor and beta-endorphin and cortisol concentrations in plasma. Decline of the hormone concentrations in the early postpartum period.

In 38 women with uncomplicated vaginal delivery at term, the different pain intensities during spontaneous labor were correlated to the plasma beta-endorphin and cortisol concentrations simultaneously examined. The pain intensities subjectively assessed were numerically categorized. The women in labor categorized to pain intensities 0 to III were in comparable stages of cervical dilatation. The hormone concentrations were measured by means of radioimmunoassay. The lowest hormone levels were found after abolition of pains of labor by epidural anesthesia: beta-endorphin 42 pg/ml, cortisol 318 ng/ml (mean values). The hormone concentrations rose progressively with increasing intensities of labor pain. The highest concentrations were observed in the first few minutes after delivery i.e. immediately after cessation of the extreme pains of expulsive labor: beta-endorphin 118 pg/ml, cortisol 449 ng/ml. Statistically significant, positive correlations were calculated between beta-endorphin and cortisol concentrations in plasma and the self-reported pain intensities (p less than 0.001 and p less than 0.01 resp.). Thus, highly elevated beta-endorphin levels in plasma do not abolish pain, probably they modulate it. Within the first four hours postpartum the concentrations of the two stress-stimulated hormones dropped rapidly. The endorphin level fell from 118 pg/ml immediately after delivery to 38 pg/ml in the above mentioned period, the cortisol level from 449 ng/ml to 302 ng/ml. One to three days after delivery the beta-endorphin and cortisol concentrations in maternal plasma were largely normalized, this means they then approximately corresponded to the values being found in nonpregnant women under normal conditions.