By Henci Goer
In October, Author Henci Goer wrote an article for Science & Sensibility, Epidural Anesthesia: To Delay or Not To Delay – That is the Question – examining the impact of the timing of an epidural on labor and birth. Today Henci looks at some new research, Epidural analgesia in labour and risk of caesarean delivery which seeks to determine whether receiving an epidural at all impacts the likelihood of a cesarean delivery. Lamaze International has a great infographic on epidurals that you also may find very helpful. – Sharon Muza, Community Manager, Science & Sensibility.
Let’s start with a bit of background for those of you who didn’t personally live through the early controversy over whether epidurals increased the cesarean rate. As epidurals began to achieve popularity in the late 1970s and 1980s, one researcher sounded the alarm when he and his group published a study of 714 first-time mothers showing that even after excluding women with big babies and women whose labor pattern was abnormal prior to having an epidural, epidurals remained a potent factor in cesarean rates for delayed progress (Thorp 1989). Everyone pooh-poohed his finding on grounds that observational studies can’t truly determine whether epidurals lead to more cesareans or women experiencing more prolonged, painful labors, and therefore at higher risk for cesarean, were more likely to want epidurals. The “chicken versus egg” question, they argued, couldn’t be resolved without a randomized controlled trial (RCT), and it wasn’t likely that women would agree to be assigned by chance to have an epidural or not. In point of fact, that same year saw publication of a small Danish RCT (107 women, 104 of them first-time mothers) (Philipsen 1989). It reported that having an epidural nearly tripled the cesarean rate (16% vs. 6%) for “cephalopelvic disproportion” despite no clinical evidence of CPD being a requirement for inclusion. The investigators ignored this, however, concluding only that instrumental vaginal delivery rates were similar, and epidurals provided better pain relief. In any case, the anesthetic dose was much higher than was already becoming the norm, so it could be reasonably argued that the trial’s findings wouldn’t apply to modern-day practice.
Thorp, meanwhile, took up the RCT challenge. He and his colleagues carried out an epidural versus no epidural trial in 93 first-time mothers and found that epidurals did, in fact, lead to cesareans (25% vs. 2%), not vice versa (Thorp 1993). That bit of unwelcome news precipitated a stampede to perform more RCTs, and when enough of those had accumulated, to a series of systematic reviews pooling their data (meta-analysis), of which the Cochrane review, Anim-Somuah et al. (2011), is the latest. These reached the more comfortable conclusion that epidurals didn’t increase likelihood of cesarean, and pro-epiduralists breathed a collective sigh of relief and went back, if they had ever stopped, to unreservedly recommending epidurals. (This rather sweeps under the rug the other problems epidurals can cause, but that’s a topic for another day.)
Weaknesses of the “Epidural” vs. “No Epidural” Trials
The finding that epidurals don’t increase cesareans is puzzling because they increase likelihood of factors associated with them (Anim-Somuah 2011). For one thing, they increase use of oxytocin to augment labor, which implies they slow labor. For another, more women run fevers, and it stands to reason that a woman progressing slowly who starts running a fever is a likely candidate for cesarean. For a third, the difference in fetal malposition (occiput posterior) rates at delivery comes close to achieving statistical significance, meaning the difference is unlikely to be due to chance. Persistent OP is strongly associated with cesarean delivery (Cheng 2006; Fitzpatrick 2001; Phipps 2014; Ponkey 2003; Senecal 2005; Sizer 2000). Epidurals even increase cesareans for fetal distress by 40%, although the absolute difference didn’t amount to much (1 more per 100 women). Could a difference exist and meta-analysis of RCTs fail to detect it?
A string of well-conducted observational studies over the years have suggested that they could (Eriksen 2011; Kjaergaard 2008; Lieberman 1996; Nguyen 2010), the most recent of which is a very large, very convincing study published last fall (Bannister-Tyrrell 2014). Its authors point out, as have others before them, the weaknesses of the RCTs, weaknesses serious enough to nullify their results or make them inapplicable to typical community practice (external validity).
To begin with, in most trials, substantial percentages of women allocated to the non-epidural group ended up having epidurals, and some women allocated to the epidural group ended up not having one. Since RCTs analyze results according to group assignment (to do otherwise would negate the point of random assignment, which is to avoid bias), not what actually happened, this diminishes differences between groups. In addition, trials were mostly confined to women with no medical or obstetric complications who were treated according to strict protocols for labor management and indications for cesarean delivery. Neither is the case in most hospitals. To these I would add that many trials lumped together first-time mothers and women with prior births when reporting outcomes. First-time mothers are much more susceptible to factors that impede progress, so including women with prior vaginal births can make it appear that epidurals are less problematic for first-time mothers than they really are. In addition, three of the trials were carried out in a hospital where participants were mostly attended by midwives, and cesarean rates were much lower than is common for women attended by obstetricians.
All of this means that any null results in meta-analyses of the trials can be taken with a grain of salt, any findings of significant differences probably represent a minimal value, and first-time moms may be harder hit than appears. To cite one example, Anim-Somuah (2011) reported that 5 more women per 100 having epidurals had a malpositioned baby at delivery (18% vs. 13%) in the 4 trials reporting this outcome, a difference, as I said, that just missed achieving statistical significance. But when I confined results to the two trials in first-time mothers alone in which 10% or fewer of the women in the “no-epidural” group had an epidural, the gap widened to 9 more per 100 (11% vs. 2%).
Summary of the Bannister-Tyrrell (2014) Analysis
Bannister-Tyrrell and colleagues (2014) drew their population from a database of 210,700 Australian women with no prior cesareans who were laboring at term with a singleton, head-down baby. A strength of the database was that, unlike most, it distinguished epidurals for labor from epidurals for delivery. Using a long list of factors, investigators constructed a propensity score for how likely a woman was to have an epidural, matched women according to their score, and compared results according to whether women with the same score had or didn’t have an epidural. Matched controls were found for 52,600 women who had an epidural and were found across the full range of propensity scores. Women having epidurals were 2.5 times more likely to have a cesarean (20% vs. 8%), or put another way, 12 more women per 100 having epidurals had a cesarean (absolute excess), which amounts to 1 additional cesarean for every 8.5 women having an epidural (number needed to harm). Among first-time mothers, women having epidurals were 2.4 times more likely to have a cesarean. Study authors didn’t provide cesarean rates for this subgroup, but the raw cesarean rates overall were 18% in first-time mothers versus 2% in women with prior births, so the effect on this more vulnerable population could be dire.
But there’s still more. Investigators further adjusted for confounding factors not captured in their database. These included differences in health-care settings (same state but not same city), care provider (women without epidurals are more likely to be attended by midwives), and for confounding interventions more likely with epidurals (continuous fetal monitoring). Relative risk of cesarean with an epidural remained at 2.5. Investigators then adjusted for the association between occiput posterior baby and cesarean by setting estimates of the risk ratio to exceed the strongest associations reported in the literature, and they assumed that the prevalence of severe labor pain was 3 to 4 times higher in women having epidurals. Factoring these into their statistical analysis reduced the risk ratio, but women having epidurals still were 50% more likely to have a cesarean. This means that with a baseline cesarean rate of 8% in women without an epidural, 12% of women with an epidural will have one or 4 more women per 100 or 1 more cesarean for every 25 women.
At the very least we cannot assure women with confidence that epidurals don’t increase the likelihood of cesarean. For this reason and because of their numerous other drawbacks and considering that comfort measures and other strategies have been shown to be both effective for most women and free of adverse effects (Declercq 2006; Jones 2012), women may want to make epidurals Plan B rather than Plan A. That being said, whatever their choice, women can minimize their chance of cesarean—with or without an epidural—by choosing a midwife or doctor whose policies and practices promote spontaneous vaginal birthhttp://www.lamaze.org/HealthyBirthPractices.
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Bannister-Tyrrell, M., Ford, J. B., Morris, J. M., & Roberts, C. L. (2014). Epidural analgesia in labour and risk of caesarean delivery. Paediatr Perinat Epidemiol, 28(5), 400-411.http://www.ncbi.nlm.nih.gov/pubmed/25040829
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About Henci Goer
Henci Goer, award-winning medical writer and internationally known speaker, is the author of The Thinking Woman’s Guide to a Better Birthand Optimal Care in Childbirth: The Case for a Physiologic Approach, She is the winner of the American College of Nurse-Midwives “Best Book of the Year” award. An independent scholar, she is an acknowledged expert on evidence-based maternity care.