Plasma corticotropin-releasing hormone, β-endorphin and cortisol inter-relationships during human pregnancy

To investigate the dynamic relationships among corticotropin-releasing hormone (CRH), β-endorphin (βEP), cortisol and obstetric events during pregnancy, blood samples were collected from 193 women at 28 weeks, 38 weeks, during labour and on the second postnatal day. Cord blood at delivery was also obtained. We found that: (1) Maternal plasma CRH, βEP and cortisol rose from 28 to 38 weeks. (2) During the third trimester maternal plasma CRH and βEP were correlated (r = 0.30, p < 0.001). (3) During labour, no correlations were found among maternal plasma CRH, βEP and cortisol. (4) Maternal CRH at labour and the duration of labour were not correlated. (5) Maternal plasma CRH tended to be higher in women who delivered early (more than seven days prior to estimated date of confinement [EDC]) relative to those who were on time (within seven ddays' EDC) or late (greater than seven days after EDC). (6) CRH in maternal plasma at labour and cord blood were correlated (r = 0.29, p < 0.05) as were maternal and fetal βEP (r = 0.43, p < 0.001). (7) Fetal obstetric difficulty was correlated with fetal βEP (r = 0.54, p < 0.001). Our findings support the hypothesis that maternal plasma CRH regulates maternal βEP during the third trimester, but other factors are involved during labour and in response to maternal obstetric stress.