In Induction of Labor

Once again the internet is abuzz over a study concluding that inducing labor doesn’t increase the cesarean rate, this time in week 39 in 1st-time mothers age 35 or older. The justification for the study is that the stillbirth rate in older women at 37 wks and beyond is the same as the rate for all women at 41-42 wks, at which point induction has become the norm. Inducing older women at 39 wks would therefore make sense provided it doesn’t have adverse effects such as increasing the cesarean rate. Let’s take a look.

Investigators randomly assigned 619 1st-time mothers aged 35 or more who had reached 36 completed weeks either to induction in the 39th wk or to “expectant management,” which wasn’t, exactly, because it included not only inducing (or performing a cesarean) for indication but elective induction at 41 weeks or more. All women were carrying one, head-down baby and had no contraindication for vaginal birth or expectant management. Results were analyzed according to “intention to treat,” meaning that women were kept in their original groups regardless of what actually happened. Cesarean rates were virtually identical (32% induction vs. 33% expectant management), and instrumental vaginal delivery rates were similar (38% induction vs. 33% expectant management). Maternal and newborn complication rates did not differ between groups. The investigators concluded: “Among women of advanced maternal age, induction of labor at 39 weeks of gestation, as compared with expectant management, had no significant effects on the rate of cesarean section and no adverse short-term effects on maternal or neonatal outcomes.”

So what’s the problem?

To begin with, the study’s premise. Stillbirth statistics are based on large population samples and don’t take into account variations in risk within the population. Older women are more likely to have health issues that increase the likelihood of stillbirth in older women overall, but it doesn’t follow that healthy older women are equally at risk.

Second, 20% of the group assigned to induction began labor spontaneously, and fully half (49%) of the group assigned to expectant management were induced. Forty percent of these inductions were elective inductions either because women had reached 41 wks or because they requested it. If inducing labor increases the cesarean rate, the large crossover rates would diminish the difference between groups.

This brings us to the overarching problem: medical-model management. Older women having a first baby might be more likely to require labor induction or a cesarean or instrumental vaginal delivery, but half of this group of low-risk women were induced and only one-third gave birth by their own efforts. We don’t have rates from a comparable population receiving physiologic care, but it’s a safe bet that you’d see better statistics than these.

Trials rooted in the medical model often amount to, “Which is better: the frying pan or the fire?”, closing the door on the possibility that neither is very good and the recognition that the model itself is problematic. Then the studies pile up, mutually reinforcing each other, until it accumulates into a seemingly overwhelming body of evidence favoring intervention. This happened with management after birth to control bleeding. It’s happening now with elective induction, but as De Vries & Lemmens (2006) wrote:

“Our evidence suggests that mainstream obstetric science follows mainstream obstetric practice. A patient and expectant approach to birth…where all is considered normal until proved otherwise, produces a science that proves intervention to be unnecessary. Alternatively, an aggressive approach to birth…, where birth is regarded as normal only in retrospect, generates a science that demonstrates the need for monitoring and intervention” (p. 2704).”

And what we have here is a textbook example of that process at work.

The Take-Away: Older 1st-time mothers with care providers who practice medical management will be no worse off being induced at 39 wks. That is not to say that they won’t be much better off with care providers who provide physiologic care.

De Vries R, Lemmens T. The social and cultural shaping of medical evidence: case studies from pharmaceutical research and obstetric science. Soc Sci Med 2006;62(11):2694-706.

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