Birth centre trials are unreliable

To the Editor: The 2005 Cochrane review Home-like versus conventional institutional settings for birth1 has been cited in the public media to claim that birth centres are less safe than labour wards as there was an increased risk of a baby dying during or immediately after childbirth.2

This “headline-grabbing” statement is false. Firstly, this finding from the systematic review did not reach statistical significance.1 Secondly, the outcomes reviewed were related to the allocated place of birth, not the care provided. This fact is critically important, as 48% of women who were booked to have their baby in a birth centre did not give birth there.1 This is a predictable effect of the intention-to-treat principle. However, such high rates of “treatment contamination” negatively affect confidence in the study results.3 Additionally, the vast majority of baby deaths examined in the Cochrane review happened before labour and thus had nothing to do with care during childbirth.

One might wonder whether there was a real increased perinatal mortality rate resulting from delayed transfers from birth centres.1 The analysis found 41 deaths in total, but only six that occurred in normally formed babies who reached term (these are the only babies who are eligible to be born in a birth centre). Three of these deaths were associated with birth centre care, and three with standard labour care.

The interpretation of this Cochrane review raises questions about the validity of the underlying randomised controlled trials. In this experimental design, researcher control should ensure that people receive the specific treatment that was planned for them (treatment fidelity).4 The Cochrane handbook gives no guidance as to how to evaluate either the quality of the researchers’ definition of the planned treatments, or the fidelity between the treatments provided and the researchers’ plan.3 Most of the trials that formed the basis of the Cochrane review did not adequately define their treatments, nor adequately control the treatments provided to either group. It is not clear how the birth centre trials could sensibly be considered to have been scientifically controlled. The reviewers attempted to deal with this critical point by claiming that they were looking only at the effect of the “setting”, but their question clearly states that they were examining the effect of “care within a setting”.1

We conclude that the Cochrane review of the setting for birth is unreliable because of the weaknesses of the underlying trials. Rather than using questionable research to attack birth centres, it would be more constructive to engage in rigorously designed research that could provide robust evidence on the safety of all forms of maternity care, including standard medical care.