[Maternal plasma beta-endorphin levels during labor in relation to maternal obesity]

The relationship between maternal plasma levels of beta-endorphin (beta-Ep) during labor and various obstetrical factors was investigated in 115 healthy pregnant women. beta-Ep was determined by radioimmunoassay using double-antibody RIA kit (INCSTAR Corporation, Stillwater, M'S.). The results were as follows: (1) The primiparous women showed a significant increase of maternal plasma levels of beta-Ep at delivery compared with the multiparous women. In addition, the group of women whose Bishop's score at the onset of labor was 5 points or less showed a significant increase of maternal plasma levels of beta-Ep at delivery compared with that in the group of women whose Bishop's score was 6 points or more. (2) The increase in maternal plasma levels of beta-Ep during the first and the second stage of labor was significantly higher in obese women (pre-pregnancy BMI > or = 24) than in normal weight women (pre-pregnancy BMI < 24). In normal weight women in pre-pregnancy, the group of women whose weight gain during pregnancy was 11kg or more showed a significantly higher increase of beta-Ep compared with that in the group of women whose weight gain was less than 11 kg. These results suggest that a stressful delivery caused a significant increase of maternal plasma levels of beta-Ep during labor. Moreover, obesity and marked weight gain during pregnancy caused a remarkable increase in beta-Ep probably due to latent dystocia.