There is a widely held belief that induction of labor increases the risk of c-section. This is something that has been widely promoted by many OB/GYNs, nurses, midwives, doulas, and patients alike. I can not tell you how many times I have heard, “Don’t let them induce you.”
I think that so many health care professionals bought into the mythology of induction increasing c-section risk because it was one of those unreferenced things written in a textbook in the 1960s that was perpetuated in so many other textbooks and lectures and on ward rounds and to patients that it became gospel instead of science. It brings to mind the Richard Feynman quote, “Science is the belief in the ignorance of experts.”
A retrospective study from 2013 looking at over 350,000 women delivering in California between 37 and 40 weeks gestation questioned this dogma. The study looked at elective inductions (meaning no medical indication) and found that at each week of the pregnancy the risk of a c-section was significantly higher in the non induction group (expectant management, or allowing labor to start on its own) versus the induction group. The relationship was most robust for multiparous women (women who had been pregnant before), but even held for women in their first pregnancy. This study is also interesting in that it challenges the notion that elective induction before 39 weeks increases NICU admissions (it did not in this study). However, this is a retrospective study and thus saddled with all the problems that brings to the research table.
Fortunately, there are prospective studies to look at. There are actually 157 randomized trials of sufficient quality to review comparing elective induction vs. no intervention and c-section rates (which surprised me to no end, but then again this isn’t my field of study). These trials combined enrolled over 31,000 women and have now been evaluated in a meta-analysis just published in the Canadian Medical Association Journal. What this careful review of the data shows is induction of labor actually reduces the risk of c-section by 12%. Looking specifically at low-risk women with no medical indication for induction when labor was induced the c-section rate was by 19% lower. Labor induction also had a “reduced risk of fetal death (RR 0.50, 95% CI 0.25–0.99; I2 = 0%) and admission to a neonatal intensive care unit (RR 0.86, 95% CI 0.79–0.94), and no impact on maternal death (RR 1.00, 95% CI 0.10–9.57; I2 = 0%).”
Looking at the data a bit closer the positive effect on reducing c-sections was seen only when prostaglandin E analogues were the method of induction (the main method of induction in Canada, US, and UK). When the method of induction was aminiotomy (rupturing membranes) or oxytocin then there was no impact on c-section. Another fascinating piece of information is that induction has more benefit for an unfavorable cervix! When the cervix was favorable induction had no impact on c-section rate, but when the cervix was unfavorable the c-section rate dropped by 13% with induction. Maybe an unfavorable cervix has less to do with not being ready for labor and more to do with a problem getting ready for labor (a problem that prostaglandins can potentially overcome?)
What does this tell us?
1) The idea that induction of labor increases the risk of c-section needs to be discarded from the lexicon. Completely. Anyone who tosses around the idea that induction with prostaglandins leads to c-sections is spouting mythology not science. It doesn’t matter how many women you may have seen get a c-section after being induced or what Ricki Lake says, personal recollection is not science.
2) Induction of labor is best accomplished with prostaglandins and not amniotomy and oxytocin.
3) We don’t understand what an unfavorable cervix at term really means. Maybe we should change the term “unfavorable” as that obviously inserts bias and confusion into discussions with patients. Clearly an unfavorable cervix does not mean greater risk of c-section (i.e. a failed induction).
Isn’t science cool?
The first principle is that you must not fool yourself – and you are the easiest person to fool.