Oxytocin deficiency at delivery with epidural analgesia.

The effect of epidural analgesia on oxytocin release during the second stage of normal labour was studied by comparing 10 primigravidae who had epidurals with 10 control subjects who did not have epidurals. A significant increment in oxytocin between paired peripheral blood samples taken at the onset of full cervical dilatation and crowning of the fetal head was found in the control subjects but not in those with epidurals. Forceps delivery was required more often in the group with epidural analgesia and was associated with lower oxytocin levels at crowning. Since distension of the lower birth canal and stimulation of pelvic autonomic nerves leads to oxytocin release, and the need for forceps associated with epidurals can be reduced by oxytocin, these differences are attributed to the lumbar epidural block.