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Epidural and the baby

Date: July 13th, 2013

“Will epidural harm my baby?” is a common question asked by expectant mothers, and childbirth experts are quick to point out possible complications and undesirable effects. However, research suggests that the effect of epidural on the baby is in fact beneficial.

In the recent issue of the International Journal of Obstetric Anesthesia the editor, Prof. Felicity Reynolds, makes an important point: it is generally assumed by lay people and many medical professionals that any form of pain relief in labor that involves drugs must be harmful for the baby, with epidural – being the most invasive – being the worst. This belief is reflected in most sources of information presented to patients. As the result, vast majority of sources of information about labor epidurals accentuate negative side-effects and possible complications. In the “Frequently asked questions” section of most childbirth education websites the answers to the question “How will epidural affect my baby?” are limited to undesirable effects. Moreover, more often than not these answers contain false statements.

Yet the benefits of labor epidural for a newborn baby have been described in many clinical studies literally decades ago. This article is the rehash of parts of Prof. Reynolds’ review that focuses on the benefits of labor epidural for the baby1.

Effects of labor pain on the mother and the baby

Everyone knows that a woman in labor breathes harder than normally. This hyperventilation is a normal response to severe pain, incidentally, also encouraged by midwives. However, as a result of increased respiration the concentration of carbon dioxide in a woman’s blood drops significantly. As carbon dioxide is the substance that drives normals breathing, once the contraction and its accompanying pain stop, a woman’s respiration respiration decreases, leading to significant decreases in oxygen content in the blood. This effect is more pronounced when opioids (pethidine, meperidine, morphine) are used for relieving pain.

During increased respiration the concentration of physiological acids in the blood of the mother decreases and pH increases. As pH is kept within very narrow physiological ranges, the body responds by producing acids, which may be readily transferred to the fetus and in turn increase the acidity of its blood.

Decrease in carbon dioxide causes vasoconstriction of the arteries, including those that supply blood to the uterus.

Decrease in carbon dioxide and pH reduces the transfer of oxygen to the fetus. This has been convincingly demonstrated in experiments on sheep. When animals hyperventilated oxygen content in the blood taken from the fetus was reduced. Slowing respiration down to normal levels restored oxygen content.

Pain is also accompanied by the production of stress hormones, such as adrenaline and cortisol. As a consequence, blood supply to the uterus decreases and blood glucose concentration increases, both of which are potentially unfavorable to the newborn.

Labor epidural is the most efficient method of blocking pain and the accompanying stress response, counteracting these unfavorable effects.

Epidural drugs and the baby

A proportion of any drugs given to the mother will be transferred to the fetus. The chemistry of a particular drug in this context is important, and some drugs cross the placenta better than others. The higher the dose given to the mother, the more of the drug will end up in the fetus. For some reason many midwives believe that opioid injections (pethidine, morphine) are less harmful to the mother and the baby than epidurals. The fallacy of this has been demonstrated in numerous studies, mostly with pethidine, and babies of mothers who were given opioids during labor often demonstrate negative effects, such as lower Apgar scores, reduced respiration and muscle tone, problems with breastfeeding and depression of the nervous system which is reflected in the behavior. These effects may be delayed and opioids may stay longer in the babies’ blood due to their reduced metabolism.

On the other hand, the dose of opioids in the epidural mixture is considerably lower, and their concentration in the fetus is significantly lower, in fact, close to negligible. Most commonly used opioid in epidural is fentanyl, the duration of action of which is relatively short. Because of this fentanyl is less likely to persist in the fetal blood, compared to longer acting opioids used as an injection during labor.

Benefits of epidural for the baby

The potentially negative effects of epidural on the neonate are readily quoted by childbirth experts. These are: decrease in blood pressure which may lead to the reduction of blood supply to the uterus, fever, increased need for use of forceps and prolonged labor. With the exception of the first complication on the list, the relationship between these undesirable effects and epidural are not straightforward, as they are caused by numerous factors. Each of these effects is discussed in detail in the appropriate chapter of this site.

On the other hand, the beneficial effects of labor epidural are quoted seldom, if ever, even though there are quite a few. By effectively eliminating labor pain epidural prevents hyperventilation and its physiological consequences, such as decrease in blood oxygen levels and vasoconstriction of uterine blood vessels. Moreover, the same mechanism that occasionally leads to the reduction in blood pressure – blocking of sympathetic nerve fibers – leads to active vasodilatation of uterine arteries, improving blood flow to the fetus.

Another often quoted potentially harmful side-effect of the epidural on the neonate is the transfer of drugs in the epidural mixture across the placenta. However, in moderns epidurals local anesthetics and opioids are used in low concentrations, and the amount of drugs transferred to the fetus are negligible and don’t lead to negative consequences.

The wellbeing of the newborn is affected by numerous factors, and it is difficult to single out the effects caused by epidural only. However, several clinical studies have shown that epidural is indeed beneficial to the newborn babies.

Fewer babies die because of epidurals

A study conducted in the UK in the seventies, the decade when the use of labor epidural was rapidly expanding, has demonstrated interesting results2. In those days epidural was used preferentially in high-risk labors. These labors are associated with a higher rate of complications, including neonatal mortality; therefore one would expect more deaths among newborns in the epidural group. On the contrary, deaths in the first week of life were considerably rarer in babies born from mothers who received labor epidurals: 1.1% versus 10.3%. The difference was most remarkable among babies with low birth weight, below 2.5 kg. The authors commented that this difference could be explained by more frequent use of forceps in mothers with epidurals. At the very least, there was no increase in neonatal death in either normal or underweight babies. Other early surveys mentioned in the Prof Reynolds’ review also confirmed a reduced mortality among high-risk babies, such as twins and breech deliveries, after labor epidural.

In the last few decades the death rate of babies has fallen dramatically, largely because of a more interventional approach to higher risk pregnancies by obstetricians, and neonatal mortality is not useful when assessing effects of epidurals on the fetus.

Apgar scores

The Apgar score was developed in 1952 by Virginia Apgar, a renowned pediatric anesthesiologist, for quick assessment of newborns. It is based on five criteria: skin color, pulse rate, reflexes, muscle tone and breathing, each given a value from 0 to 2. The scoring is done at one and five minutes after birth. Scores 7 -10 are considered normal, 4 – 6 low and 3 and below critically low. The purpose of the Apgar score is to determine whether the newborn needs immediate medical attention.

Numerous studies comparing labor epidural with other methods of pain relief in labor, as well as the current Cochrane database review demonstrate higher Apgar scores among neonates born from mothers who received epidural during labor. However, in most of these studies the women without epidurals were given systemic opioids. Therefore, it is possible that these results do not accurately reflect the beneficial effects of labor epidural analgesia, but rather, the negative effects of systemic opioids.

Acid-base status of the newborn

When oxygen supply to the tissues is compromised, cells produce lactic acid, which results in acidosis, or increased acidity of the blood. This is accompanied by a drop in the concentration of bases, substances produced by the body to decrease this acidity. By the 1970-s the technology evolved to the point where the assessment of these compounds in the blood – acid-base status – became routine clinical practice and became the primary test of wellbeing of the neonate during and after labor.

In 1974, three studies were published where the blood was sampled from babies during labor. One of these studies was randomized. They showed that labor epidural reduced the decline of carbon dioxide in the mothers’ blood, reduced acidosis, and reduced the concentration of lactic acid in the blood of the fetus. It also significantly mitigated the fall in pH (increased acidity) that typically occurs during the second stage of labor. These favorable findings were largely ignored.

In 2002, a meta-analysis was published which was based on acid-base measurements of more than 2000 babies in twelve studies. It confirmed that the acid-base status of neonates was significantly improved by epidural analgesia in labor. The benefits were observed with both old-fashioned epidurals using higher concentration of local anesthetics and more modern, using low dose ropivacaine. Once again, the comparison group consisted of patients who received systemic opioids, so the question remains: was epidural beneficial or were rather opioids detrimental to the fetus.

To answer this question a research group from Dallas conducted a study where they compared the acid-base parameters of babies born from mothers receiving labor epidural with those who received no pain relief at all4. Neonates in the epidural group had higher carbon dioxide and base excess, both of which suggested the beneficial effects of labor epidural on acid-base status, and not simply the harmful effects of opioids.

Epidural does no harm to the babies

Prof. Reynolds’ review is based on 135 studies. The vast majority of them show no negative effects of epidural analgesia on newborns. Several trials, in particular methodologically rock solid acid-base studies, actually show significant benefits. Yet many sources of epidural information available to expectant mothers – Internet sites, the media and even some medical professionals – emphasize the problems rather than the benefits. Epidural is often presented as a necessary evil, sort of: “epidural is effective for controlling pain, but…” Sure, labor epidurals have their set of complications, sometimes severe, and undesirable effects, just like any other medical procedure. On the other hand, the study from Dallas clearly demonstrates the measurable benefits of epidurals versus so called natural birth, with no pain relief at all. It is time for birth educators to get their knowledge up to date and start telling their patients that labor epidural can actually be good for their babies.

References:

1. Reynolds F. Labour analgesia and the baby: good news is no news. International Journal of Obstetric Anesthesia (2011) 20, 38-50.

2. David H, Rosen M. Perinatal mortality after epidural analgesia. Anaesthesia 1976; 31:1054-9.

3. Reynolds F, Sharma S, Seed PT. Analgesia in labour and funic acid-base balance. A meta-analysis comparing epidural with systemic opioid analgesia. BJOG 2002; 109:1344-53.

4. Schocket M, Garrison R, Wiley J, Sharma S. Epidural analgesia has a favorable effect on funic base excess compared to no analgesia during labor. Anesthesiology 2005; 102:SOAP abstract A40.

Image: FreeDigitalPhotos.net

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Dr. Eugene Smetannikov is a practicing anesthesiologist with the interest in obstetric anesthesia. He is the author of the most comprehensive book on the subject, The Truth About Labor Epidural

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