How Does an Epidural Affect the Duration of Labor?

Let’s address the duration of labor comparing women who choose to give birth naturally to women who have an epidural.

First, not all women are alike, not all labors are alike, and not all anesthetics are alike.  For this reason, there is tremendous variability in the duration of labor no matter how you have your baby.

That being said, the scientific literature reviewed by Drs. Anim-Somuah, Smyth, and Jones for the Cochrane Collaboration in their document Epidural versus non-epidural or no analgesia in labour concludes that epidural anesthesia will prolong your labor by about 14 minutes.  The reviewers looked at eleven articles that examined the first stage of labor and thirteen articles that considered the second stage of labor.  The first stage of labor is the time it takes to achieve complete dilation and effacement, and the second stage is the time it takes to deliver the baby once you are completely dilated.  Concerning the first stage of labor, the authors concluded that , “There was no evidence of a significant difference in this outcome.”  And about the time it takes after reaching complete dilatation to deliver the baby they state, “Women with epidural analgesia had a statistically significant longer second stage of labour.”  Women with epidurals labor about 14 minutes longer, on average, than women having natural childbirth.

Why should this be true?  We can’t be sure why women who ask for epidurals labor longer.  It may be that more painful labor is itself associated with longer labor.

The process of receiving an epidural may prolong labor.  One of the side effects of an epidural is a tendency for the woman’s blood pressure to drop.  In order to prevent the drop in blood pressure anesthesiologists and anesthetists administer extra intravenous fluid just prior to placing the epidural.  This intravenous fluid may dilute the naturally secreted oxytocin that is the driver of the uterine contractions.  When one observes the graph of the uterine contractions they tend to occur less frequently immediately after the fluid administration, and return to their normal pattern after about 20 minutes.  It takes about 20 minutes for the kidneys to clear that additional fluid from your blood stream.

Epidural anesthesia not only relieves your pain, but it affects the ability of your skeletal muscles to function normally below the level of the anesthetic.  We do not allow women to walk after epidurals at our hospital even with very “light” epidurals because the ability to walk is impaired and the woman may fall.  The abdominal muscles may become weaker also if the anesthetic is high enough to affect these muscle.  If the abdominal muscles are weak it may be harder to push out the baby.  As the time for delivery approaches the anesthetic may be reevaluated and decreased if need be to allow for better pushing.  Usually this is not a problem.

Some people believe that a woman’s pelvic floor muscles must be functioning well to help guide the baby’s head out of the pelvis and into the birth canal.  With an epidural these muscles also are affected so that this help is not available.

What do we see clinically?  (These comments reflect what we commonly see in the delivery room, so do not represent scientific study.)  When women have epidurals they naturally (not in the natural childbirth sense) relax.  Some women who are experiencing unmedicated labor cannot relax their pelvic floor muscles.  These muscles must relax so that the baby can pass through them.  So until they are able to relax the results of the work of their labor may not be evident…they won’t dilate.  When the woman in natural childbirth finally “surrenders to the pain” she is able to relax the pelvic floor and allow the baby to descend, her cervix to dilate, and deliver.  Very often women who have tried to deliver naturally and opt for an epidural deliver rapidly after the epidural.  I believe this happens because she has been doing the hard work of labor, but her unrelaxed pelvic floor muscles won’t allow her to progress.  The epidural does the same thing as the women who can break through the pain herself.


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