THE EFFECT OF EARLY LABOR, MATERNAL ANALGESIA AND FETAL ACIDOSIS ON FETAL PLASMA OXYTOCIN CONCENTRATIONS

Objective To determine the effect of early labour, maternal analgesia and fetal hypoxia on circulating fetal oxytocin concentrations. Design Prospective observational study. Setting Delivery suite in a District General Hospital. Subjects Fifty women at term who did not require ox ytocin administration or more than one form of analgesia. Study groups : vaginal delivery with (1) no analgesia, (2) pethidine, or (3) epidur al analgesia. Caesarean section under regional analgesia (4) prior to, and (5) after the onset of labour. Interventions Samples of blood wer e collected from the umbilical artery (UA) and umbilical vein (UV) imm ediately after fetal delivery prior to placental separation or oxytoci c administration. Main outcome measures Plasma oxytocin (OT) concentra tion, umbilical vein pH, cystine aminopeptidase activity. Results The geometric mean UA-OT was significantly greater than UV-OT in all group s and was not altered by pethidine; however, epidural administration i ncreased the UA-UV difference. The UA-UV difference at caesarean secti on was not significantly altered by the onset of labour. There was no correlation between UV pH and UA-UV plasma oxytocin. Cystine aminopept idase activity was not detectable in UA and UV plasma. Conclusions Fet al OT production is increased by epidural but not by pethidine analges ia. It is not influenced by the onset of labour or fetal hypoxia.