The effect of early labour, 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 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.