Plasma oxytocin levels in women during labor with or without epidural analgesia: a prospective study.

Background: Epidural analgesia (EDA) has been reported to prolong labor. Whether this is by interference with endogenous oxytocin release or other mechanisms is unclear. With increasing numbers of women receiving an EDA, it is important to study its effects on labor. The aim was to study the concentration of plasma oxytocin and the progress of labor in women with and without EDA.

Methods: Thirty-four full-term women in spontaneous labor were included, 17 with epidural and 17 controls, matched for cervical dilatation and parity. Oxytocin was measured by radioimmunoassay before analgesia, 60 min later and after placental discharge. No oxytocin augmentation was given during the first hour.

Results: EDA during labor was associated with a fall in plasma oxytocin. There was no difference in plasma oxytocin levels between the groups at inclusion. One hour later, oxytocin concentrations had decreased in the epidural and increased in the control group (Student's t-test, p = 0049). The change in oxytocin levels between the first and second sample differed significantly between the groups (ancova, p = 0.028). No difference in cervix dilatation between the groups 1 h after inclusion was noted, but women with EDA had a longer labor compared with those without, especially those with epidural and oxytocin augmentation during the later phase of the first stage of labor.

Conclusion: EDA during labor may interfere with the release of plasma oxytocin, which may be one mechanism behind prolongation of labor. Larger studies are needed to clarify the effects of epidural analgesia and the role of oxytocin during labor.