Does epidural increase the risk of cesarean section?

Does epidural increase the risk of cesarean section?

There is no evidence that labor epidural increases the risk of cesarean section. Neither it matters if epidural is started early or late in labor.

Emergency caesarean section probably appears in every pregnant woman’s nightmare. Labor itself is a complex, unusual, uncomfortable and more often than not painful experience. The very idea of having epidural is to make labor painless and comfortable. But if it may delay progress of labor or cause fetal distress to the point that an emergency caesarean is needed, is it really worth it? This chapter will explain the state of affairs with epidurals and caesareans.

Theoretically, epidural anaesthesia may increase the risk of caesarean section in several ways. It may lead to the decrease in blood pressure which, in turn, decreases blood supply to the uterus and causes fetal distress. Fetal distress, in turn, is an indication for urgent caesarean section. Epidural induces some degree of muscle weakness and, in theory, slow the progress of labor to the point that the baby may only be delivered surgically. Strong epidural block may interfere with the woman’s ability to push during the second stage of labor, in which case again, surgery is necessary. This topic has been hotly debated, and complex literature reviews and are performed on regular basis on this topic in order to keep the evidence up to date.

As it is the case with studying pain in labor, research on the effects of epidural analgesia on outcomes of labor is also problematic. Randomized controlled studies remain the golden standard of such research, but are difficult to design and conduct for various reasons. Ideally such trial would randomly allocate patients to receive either epidural anesthesia or other method of pain control and then compare the rates of cesarean section. In real life though the patient has the right to change her mind and “cross over” to another method of analgesia, and it would be unethical to deny her this option. If this happens, the total number of patients required in order to get statistically significant results increases dramatically. As the research funding is often limited, this increase is not possible and the results are less reliable.

Another way to compare cesarean rates is through observational studies. The easiest way to do such study is to select equal groups of patients who had cesarean section and those who delivered vaginally and compare which group had more epidurals. Such studies have value, but selection bias is a problem and the results are grossly influenced by the hospital policy of epidural service. For instance, in some labor wards epidurals are given to patients who do not cope with labor well and are selected on the basis of midwives’ opinions. If clinical data shows that women receiving epidurals in this setting are undergoing emergency caesarean section more often than patients getting other methods of analgesia, does it signify that this is the effect of epidurals? Not at all, because it is equally possible that the patients going for caesareans have more difficult labor and were at higher risk of surgery, independently of receiving epidural. There are various, very complex mathematical methods that help minimize errors and biases, but the value of these trials is still lower than that of randomized studies.

Lastly, there are studies with historical controls. For instance, in many hospitals epidural service in maternity wards is not available for various reasons, most often shortage of qualified anaesthetists. Then the funding improves and the service is introduced. Comparing profiles of complications, including percentage of patients undergoing caesarean section before and after epidurals became available, allows to make conclusion regarding the risks of different techniques of analgesia. This method also has problems, because with the introduction of epidural service other aspects of obstetric care may change as well and influence the final results.

The debate regarding epidurals causing more caesareans has been going on since the beginning of use of epidurals in labor. One of the most comprehensive reviews published in 2002 identified ten randomized controlled trials that considered this question1. The association of epidural with cesarean delivery in these trials varied dramatically within these trials with relative risks (RR) ranging from 0.7 to 11.2. Relative risk is a parameter that helps to compare the influence of one factor on an outcome. For example, if we study two groups of women, one receiving epidural analgesia and another receiving nothing and find that in the epidural group 20 women out of 100 had to undergo caesarean section and in controls 16 out of 100 had surgery, relative risk is 20/16 or 1.25. Or, in other words, 25% more patients in the epidural group needed caesarean. Relative risk values above 1.0 mean increased, while values below 1.0 indicate decreased risk. Further mathematical tests have to be applied to verify the RR and make sure it is statistically significant. The reported effect of epidural on cesarean risk in various studies in the review ranged from decreasing it by 30% (RR of 0.7) to increasing it by more than 11-fold. This illustrates the difficulty of studying the effect of one intervention – epidural – on an extremely complex decision to proceed with caesarean section.

In six studies out of ten, RR was below 1.0, meaning that the caesarean rate was lower in epidural groups. In the remaining three, the RR ranged between 1.6 and 2.3. In one, well known study by James Thorp and his co-workers that included 97 women it was 11.2. Remarkably, the percentage of patients who had caesareans was also all over the place in both groups: from 3 to 18% and 25% in Thorp’s study. In the largest trial by Loughnan and co-workers conducted in 2000 and comparing 304 women with epidurals with 310 in control group there was no statistically significant difference in caesarean rate: 13% in epidural and 12% in controls3.

Observational studies showed stronger association between epidural analgesia and caesarean section. In 33 eligible studies relative risk of caesarean varied between 0.3 to 6.5, with values above 2.0 in most trials. However comparing patient characteristics in epidural and non-epidural groups makes the data less convincing. Women who chose epidural analgesia were more likely to be slightly shorter, to have larger infants and have more advanced pregnancy. Perhaps more importantly, women who went on to choose epidural were admitted to the hospital earlier in labor and dilate more slowly just after admission compared with women who do not go on to receive epidural. The choice of epidural decreased directly with greater cervical dilation at admission. In other words, the more advanced the labor, the less likely was the woman to ask for epidural. Of all observational studies only three took into account the differences between characteristics of labor process, namely the speed and the degree of progression when the epidural was started. After taking into account these factors, all three found an increase in caesarean deliveries by at least two-fold.

The review also included studies with historical controls. Three of such trials were of appropriate standard. All showed little or no increase in cesarean delivery rates between the periods when epidurals were used in labor compared with times when they were not available.

The authors of the review concluded that although many studies have noted an association of epidural analgesia with cesarean delivery, the question of whether epidural causes cesarean delivery had remained controversial. It was impossible to discern if the difference in caesarean rate was because of the epidural itself or some differences between women who receive or request epidural analgesia and women who do not. It is perfectly possible that the women who received epidurals might have the hardest labors, and would be at higher risk for cesarean delivery even without an epidural.

Randomized controlled trials at the time of the review were either too small or did not allow clear interpretation of the data. For example, the mentioned study by Thorp and colleagues found strong association between epidural and cesarean deliveries but was too small to allow definitive conclusions. Other trials had large degree of crossovers, and this made the findings virtually impossible to interpret. There were other factors that made the interpretation of the trials and making generalized conclusions difficult, and the authors stated that at the time of the review, there was no evidence that use of epidural analgesia in labor increased the risk of caesarean section.

The complexity of factors that influence clinicians’ decision to do caesarean section was very well demonstrated in the earlier review by already known to us James Thorp, whose previous study found the strongest association between epidurals and caesareans4. He discussed possible reasons for the discrepancy in the statistical data. Discussing studies with historical controls, Thorp noted that these studies must be interpreted with caution. Besides the fact that many variables affect caesarean birth rates with time, these trials often report small number of patients and are, therefore, of limited value. But he noted that there are also studies demonstrating that modifying epidural techniques with time in the same hospital have significantly affected the course of labor and the outcome of delivery. Most important modification was using a lower concentration of local anesthetic agent.

Thorp’s review was written in 1998, before the introduction of ropivacaine into general obstetric practice. Ropivacaine has unique property to affect sensory nerve fibers to larger degree than motor cells. To refresh basic physiology of nerve conduction, nerves consist mainly of two types of nerve fibers: sensory and motor. Sensory fibers are responsible for transmitting impulses, including painful stimulation, from the periphery to the central nervous system. Motor fibers carry signals from the brain to the muscles. Local anesthetics block both fibers. That’s why you cannot smile for a while after the visit to a dentist. This effect is undesirable during labor, and ideally we would like to block pain without affecting the ability to move and, ultimately, to push during the second stage. Ropivacaine is different in the sense that it has more effect on the sensory fibers, especially at low concentrations.

However, even with older local anaesthetics there was a difference in motor blockade at different concentrations, and this was reflected in Thorp’s review. He quoted the trial from the Department of Anesthesiology at Washington University in St. Louis that analyzed their outcome data using three different epidural techniques at their institution. When epidural was performed with lower concentrations of bupivacaine – local anaesthetic used most frequently in epidurals at the time – the frequency of caesareans was the same as in non-epidural group, and it increased if higher concentrations were used. This observation was confirmed by other studies.

Another factor that affected the outcome of labor was the actual technique of epidural. One study divided patients receiving epidurals into two groups. One group had epidural throughout the labor, up until the baby was born. In another, epidural was stopped during the late first stage, when the cervix was 8 centimeters dilated. The theory behind it is letting local anaesthetic effect wear off to some extent will result in better muscular strength, improved ability to push and less need for intervention. This theory was correct, and it was shown that discontinuing the epidural infusion resulted in lower caesarean deliveries.

Choice of drug also had an effect. The group of women who receiving epidurals with lignocaine had lower rates of caesarean sections than those receiving bupivacaine. The duration of anaesthetic effect of lignocaine is shorter and it wears off faster which may explain the difference.

It is clear that concentration of local anesthetic used for epidural can be reduced to a certain minimum, otherwise epidural will not work. Addition of opioids to local anesthetics helps to overcome the problem. Local anaesthetic and an opioid have synergistic action and result in better pain relief. As the result there is less chance of motor block in the second stage of labor that may interfere with the ability to push.

Summarizing the effects of epidural analgesia on the frequency of caesarean section Thorp commented that there are many factors that influence Cesarean birth rates and epidural analgesia is just one of them. Given the numerous confounding variables, it should not be surprising that the effect of epidural analgesia on Cesarean birth rates is institution-dependent or practitioner-dependent. In some hospitals, epidural analgesia appeared to have increased Cesarean birth rates, in some not. He also noted that it is important to recognize that conclusions drawn from research centers may not necessarily apply to other institutions. Overall conclusion was that it was unlikely that epidural analgesia had a clinically significant effect on Cesarean birth rates if an institution or clinician was of high clinical standard. However, if there were problems with overall care or experience and technical abilities of clinicians, then obstetric and anesthesia care providers may consider epidural analgesia and other factors as potential contributors to the excessive Cesarean birth rates. This conclusion was made in 1998.

More recently, Cochrane Database review updated in 2005 analyzed twenty trials involving 6534 women. The conclusion of the review was that there was no evidence of a statistically significant difference in the risk of caesarean section between women receiving epidurals and those who did not. The results did not change after excluding trials where more than 30% of the women did not receive the randomized treatment or received additional pain relief. Neither excluding trials on the basis of methodological quality change the conclusion. Epidural does not increase the risk of cesarean section, full stop.

Another issue that has been debated for years is timing of labor epidural. In earlier studies it was suggested that starting epidural early in labor was associated with higher rates of caesarean sections, with resulting conclusion that it should be started after cervical dilation reaches 4-5 cm. This point was reinforced in the Practice Bulletin of the American College of Obstetricians and Gynaecologists (ACOG) in 2002. It recommended that when feasible, obstetric practitioners should delay the administration of NA in nulliparous women until cervical dilation reaches 4–5 cm, and other forms of analgesia should be used until that time.

On the other hand, Practice Guidelines of the American Society of Anesthesiologists issued earlier argued that cervical dilation is not a reliable means of determining when regional analgesia should be initiated, and that regional analgesia should be administered on an individualized basis. The guidelines are contradictory, though both are based on consensus and expert opinion.

Finally, in 2006 ACOG has updated its position by a new report of consensus and expert opinion, stating that, when compared with intravenous systemic analgesia, epidural established in early labor does not increase the risk of caesarean delivery.

To reach definitive conclusion based on published evidence in 2007 Italian group of researchers conducted systematic review of existing studies on the subject. Out of twenty trials that had relevant information 9 were selected that met strict quality criteria. Selected studies have been conducted between 1994 and 2006 and included grand total of 3,320 patients. All of the studies compared women giving birth who received epidurals early versus those who either epidural late in labor, with or without other form of analgesia (opioid). Early labor was defined as cervical dilation of 4 cm or less. The conclusions of the review were as follows:

  • Early epidural given on woman’s request does not increase the risk of either caesarean section or instrumental delivery
  • Early epidural is associated with better neonatal outcome: less naloxone was used and higher umbilical cord pH values were observed in babies born from mothers given early epidural
  • Early epidural is more effective method of pain relief in labor than opioid analgesia.

The decision to perform caesarean section on woman in labor is based on many factors. In modern hospitals with appropriate standards of practice, where properly qualified and experienced obstetricians and gynaecologists are managing the childbirth, epidural analgesia does not increase the risk of caesarean delivery. There is no evidence that early epidural may increase the risk of cesarean section. Latest systematic review points out that early epidural provides more efficient pain control and is beneficial for the newborns.

References:

1. Lieberman E, O’Donoghue C. Unintended effects of epidural analgesia during labor: A systematic review. Am J Obstet Gynecol 2002;186:S31-68.

2. Thorp JA, Hu DH, Albin RM, McNitt J, Meyer BA, Cohen GR, Yeast JD. The effect of intrapartum epidural analgesia on nulliparous labor: a randomized, controlled, prospective trial. Am. J. Obstet. Gynecol. 1993 Oct;169(4):851-8.

3. Loughnan BA, Carli F, Romney M, Dore CJ, Gordon H. Randomized controlled comparison of epidural bupivacaine versus pethidine for analgesia in labour. Br J Anaesth 2000;84:715-9.

4. Thorp J. Epidural Analgesia for Labor: Effect on the Cesarean Birth Rate. Clinical obstetrics and gynaecology. Volume 41(2), June 1998, pp 449-460.

5. Anim-Somuah M, Smyth R, Howell C. Epidural versus non-epidural or no analgesia in labour. Cochrane Database of Systematic Reviews 2005, Issue 4. Art. No.: CD000331. DOI: 10.1002/14651858.CD000331.pub2.

6. Goetzl LM, American College of Obstetricians and Gynecologists, Committee on Practice Bulletins-Obstetrics: ACOG Practice Bulletin. Clinical Management Guidelines for Obstetrician-Gynecologists n. 36, July 2002: Obstetric analgesia and anesthesia. Obstet Gynecol 2002; 100:177–91.

7. Marucci M, Cinnella G, Perchiazzi G,Brienza N,Fiore T.Patient-requested Neuraxial Analgesia for Labor Impact on Rates of Cesarean and Instrumental Vaginal Delivery. Anesthesiology 2007; 106:1035–45.

8. American Society of Anesthesiologists, Task Force on Obstetrical Anesthesia: Practice guidelines for obstetrical anesthesia. Anesthesiology 1999; 95:600–11.

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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