38 weeks is too early

In New South Wales (the part of Australia around Sydney) their public health databases record not just gestational age, but the mode of delivery and whether there was an induction of labour, or labour prior to caesarean delivery. In the same part of Australia, every 3 years, during their first year of full-time schooling, children are evaluated by their teachers using a validated tool called the AEDC, which stands for Australian Early Development Census. This tool evaluates development in 5 domains: physical health and well-being, language and cognitive skills, social competence, emotional maturity, and communication skills and general knowledge.These data are also entered into a database.

Just imagine what you could do if you put the 2 databases side by side!

Well, you could do something amazing like this: Bentley JP, et al. Planned Birth Before 39 Weeks and Child Development: A Population-Based Study. Pediatrics. 2016. You could look at early term, and late preterm deliveries, and find out if having a labour induction at 37 or 38 weeks was safe, in terms of developmental outcomes.

You would have to decide what you considered to be an adverse outcome: such as being below the 10th percentile for 2 of the AEDC domains, which you would then call “developmental high risk” or DHR. This was indeed the primary outcome variable for this study, that looked at gestational age in completed weeks from 32 weeks onward, and mode of, and indication for, delivery. The authors were able to link the AEDC data from 2009 and 2012 to birth data for over 150,000 children.

Nearly 10% of all the children were considered to be developmental high-risk, DHR, and the more immature the child was at birth the higher the relative risk of being DHR, which was true up to, and including, 38 weeks. At 38 weeks there was a 6% increase in the risk of a child being DHR compared to being delivered at 40 weeks.

In other studies of late preterm births, or early term births, the reason a child was delivered early were usually unknown, which has always complicated the interpretation of the results, it was never clear if the reason which led to the early delivery was the problem, or just being born early.

This study partially addresses this, but it still remains a little uncertain why labour was induced at 38 weeks rather than later. Some of the differences that they found may be due to, for example, mothers with early or established pre-eclampsia being induced at 38 weeks, or mothers with a baby showing early signs of growth restriction. the authors have tried to address this by adjusting the relative risks for maternal hypertension and for infants being small for gestational age, which is about as good as you could do with this kind of data.


You can see from this figure, which shows the adjusted relative risks of having DHR, that there really isn’t any difference between 39 weeks, and 40+ weeks. Once you are 38 weeks or less, there are more and more children with DHR, and at each week of gestation, spontaneous labour is associated with lower risks than induction, and the highest risk is actually having an induced labour and then ending up with a C/section.

I think it is highly unlikely that the teachers were aware of the birth history of the children, which makes this assessment practically masked, and I think a very reliable evaluation of the associations between delivery and these outcomes. Of course you can never, from observational data, ascribe causation, but it is hard to think of any other reason why you would find these associations after adjustment, other than a causative link; meaning that it seems most likely that inducing labour, or doing a caesarean delivery before 39 completed weeks, interrupts cerebral development and has long-term adverse effects.

It is also interesting that, even at 40 weeks, there seem to be some risks from having an induction or from a pre-labour caesarean. Although on an individual basis the risks are small, on a population basis this is important, and this information should certainly be included in any shared decision-making about timing of induction or elective caesarean delivery.

The lesson I think from all of this, is that you should have a really good reason for inducing labour, or performing a pre-labour caesarean. The best outcomes seem to be, even if a caesarean is planned, among babies delivered after the onset of spontaneous labour.


About Keith Barrington

I am a neonatologist and clinical researcher at Sainte Justine University Health Center in Montréal
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