Inducing labor at 39 weeks - is picking your kid's birthday worth it?

Few aspects of modern medicine engender as much controversy as our labor and delivery practices. Rates of early induction of labor vary widely from country to country – even from hospital to hospital. And while some randomized trials have demonstrated that induction of labor prior to 40 weeks gestation might have favorable effects for infants with certain conditions like large-for-gestational age, we really don’t have much data on the effects of induction of labor during a normal pregnancy. But a study appearing in the New England Journal of Medicine attempts to shed light on that issue.

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Run out of 39 hospitals in England, this study randomized 619 women, all age 35 or older on their first pregnancy, to labor induction at 39 weeks, or usual care.

Why do this? Well, for one thing, induction of labor prior to the official due date is pretty common. There is, perhaps, a quality-of-life argument to be made about having the ability to more or less choose when to deliver a baby. There is also some observational data that suggests that the sweet spot for delivery is around 38-39 weeks. Prior to that, complications associated with pre-term infants go up, and much beyond that and you start to see other birth complications.

Now, this study was clearly too small to detect differences in rare outcomes like neonatal or maternal mortality, but there has been some concern that induction of labor might increase the rate of c-section.

This study saw no such increase. The rate of c-section was 32% in the induction group and 33% in the usual care group – not statistically different. There were also no differences in rates of assisted vaginal delivery or NICU admissions, and every child in the study survived to hospital discharge. One fact caught my eye, though, and I think it gives us insight into the main limitation of this trial.

There was no significant difference in birth weight between the arms of the study. You’d think that the early induction arm would at least have slightly smaller babies. But in reality, the arms just weren’t that different in terms of any measured variables. Why? Well, there were women in the usual care arm who went into labor at 38 weeks. In fact, only 222 of the 305 women in the induction group got induction of labor prior to 40 weeks of gestation, as the protocol specified.

This bias, which the authors half-jokingly describe as “non-adherence”, is due to the fact that randomization into the study could occur at any time from 36-40 weeks. If you wanted to really answer the question that the authors pose, you’d randomize everyone at 39 weeks, and if they were put in the early induction arm, induce them at or near the time of randomization.

So we need to interpret this study not as saying that early induction is safe, but that a plan for early induction is safe. This is a subtle difference, for sure, but an important one if you are discussing inducing a woman who has already hit the 39 week mark. Still, in my book, a small victory for patient autonomy is a victory nonetheless.

Should the worldwide c-section rate be 15%?

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Every pregnant woman should get a c-section.

Wait, no. No pregnant women should get c-sections.

Hmm, that doesn’t seem right either.

There are a lot of black and white things in medicine. Should we treat scurvy with vitamin C? Hard to argue against it. But there are many areas where hard and fast rules just don’t apply, and the c-section rate is a big one.

OK – we’ve decided that a 100% c-section rate is too high, and a 0% c-section rate is too low. What’s the right number? If your answer is “well, it’s too complicated to really assign a number”, you are in stark disagreement with the World Health Organization, which suggests that the appropriate rate is somewhere between 10 and 15% of live births.

Now a study appearing in the Journal of the American Medical Association suggests that that target might be too low. But I’m going to suggest that the whole idea of a target is misplaced anyway. But first, the details:

This is what’s called an ecological study. Instead of looking at the experience of individual patients, the study uses aggregate data, in this case, national c-section rates from all 194 WHO member states, and links them to that country’s maternal and neonatal mortality rates. The lowest c-section rate was 0.6% in South Sudan, likely attributable to a lack of appropriate facilities. The highest rate was 56%, in Brazil, for reasons that we can all speculate about offline.

Overall, the finding was that countries with higher c-section rates had lower maternal and infant mortality. C-section rates of less than 5% were associated with high rates of maternal mortality – about 0.4% and infant mortality – about 1.5%. These figures got better as the rate of c-section went up until the 20% c-section mark, where things sort of flattened out. In other words, no evidence of higher mortality as the c-section rate increased further.

The trouble with an ecological study is that you only have national-level data to work with. The authors adjusted for what they could – GDP for instance, but we lack information on a critical factor – complications during delivery.

The reason the 15% c-section target set out by the WHO doesn’t make sense is that it is a target that averages two different populations – women who need c-sections due to medical necessity, and women who don’t. There is evidence in the US that unnecessary c-sections increase maternal morbidity. Simultaneously, there is ample evidence that lack of access to c-section when it is necessary is a major problem in the developing world. While there are few absolutes in medicine, one could argue that the c-section rate should be 100% for women who need them, and pretty low for those who don’t. Rather than arguing whether 15% or 20% is the “right” national c-section rate, let’s turn our efforts in getting c-sections to the right people, regardless of the nation they call home.