Effect of early epidural analgesia on labor: cutting through the confusion

Jul 01, 2006

Does early regional analgesia during labor really raise the risk of C/S, compared to early systemic analgesia? The authors believe their randomized controlled trial definitively answers that question.

Many of us often encourage laboring patients who choose epidural analgesia to try to hold off receiving it as long as possible, or at least until cervical dilation reaches 4 to 5 cm.1 But should we be doing that? This recommendation is based on the finding by several studies of an association between beginning epidural analgesia early in labor and an increased rate of cesarean (C/S) delivery.2,3 For example, in one study the odds ratio for C/S in nulliparas who had analgesia initiated at cervical dilation less than 4 cm was 2.2 (95% CI; 1.4–3.4) compared to initiation at dilation of 4 cm or more.3

Here are a few possible explanations for this observation. [A woman's request for pain relief in early labor may be a marker for an unidentified risk factor(s) for cesarean delivery.] Indeed, several studies have found that women who have higher systemic opioid or epidural maintenance requirements during labor have a higher C/S rate compared to women who need lower doses of analgesic drugs.4,5 Dysfunctional labor, fetal malposition, and macrosomia may all be associated with more painful labor and a higher C/S rate.

Or could it be that regional analgesia directly or indirectly influences the progress and outcome of labor? Epidural and spinal local anesthetics may relax the pelvic musculature, leading to abnormal fetal descent and rotation or impair abdominal muscle function and reduce maternal expulsion efforts. Women randomized to traditional high-dose epidural analgesia (with 0.25% bupivacaine) were more likely to have an instrumental vaginal delivery than women randomized to low-dose (0.1% bupivacaine with fentanyl) epidural maintenance techniques, although the rate of C/S delivery was no different among the groups.6 In addition, regional analgesia alters both thoracolumbar sympathetic and sacral parasympathetic outflow from the spinal cord and relative changes in autonomic nervous system tone may influence the progress of labor.7

A clinical trial compares regional and systemic anesthesia

To definitively ascertain whether regional analgesia begun early in labor adversely affects the rate of C/S delivery compared to early labor systemic opioid analgesia, we designed and performed a randomized controlled trial (RCT) in first-time laboring women who requested analgesia in early labor.11