The effect of early labour, maternal analgesia and fetal acidosis on fetal plasma oxytocin concentrations

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Abstract
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 oxytocin administration or more than one form of analgesia. Study groups: vaginal delivery with (1) no analgesia, (2) pethidine, or (3) epidural analgesia. Caesarean section under regional analgesia (4) prior to, and (5) after the onset of labour.Interventions Samples of blood were collected from the umbilical artery (UA) and umbilical vein (UV) immediately after fetal delivery prior to placental separation or oxytocic administration.Main outcome measures Plasma oxytocin (OT) concentration, umbilical vein pH, cystine aminopeptidase activity.Results The geometric mean UA–OT was significantly greater than UV–OT in all groups and was not altered by pethidine; however, epidural administration increased the UA–UV difference. The UA–UV difference at caesarean section was not significantly altered by the onset of labour. There was no correlation between UV pH and UA–UV plasma oxytocin. Cystine aminopeptidase activity was not detectable in UA and UV plasma.Conclusions Fetal OT production is increased by epidural but not by pethidine analgesia. It is not influenced by the onset of labour or fetal hypoxia.