Part 1: Why I remain sceptical of RCTs concerning obstetric interventions in normal labour and birth
Another blog post in response to a Twitter debate .. this time concerning various RCTs currently evaluating IOL vs expectant management. We’ve been discussing three trials:
- The 35/39 trial currently being conducted in the UK (primips over age 35, at 39 wks).
- The ARRIVE trial on the books for the USA (all women, at 39 wks).
- The Dutch INDEX trial, looking at induction at 41 weeks rather than 42.
- (See also Jim Thornton’s blog on the topic, and the post from Sheena Byrom which prompted the debate.)
The questions are valid. We know stillbirth is increased, especially in certain populations, the longer a pregnancy continues. In order to make an informed decision, many women will want to know the most likely outcomes and effects of opting in or out of proposed interventions. RCTs are considered the most unbiased way of settling these issues, unsullied by the biases of women or health professionals.
The problem is, these interventions are eventually applied to a population that is, due to being human, inherently biased. Some women feel a strong preference in one direction, some in another; and some want their doctor to decide for them. Women need to consent to be randomised into RCTs, and women who are most averse to the proposed intervention simply decline consent. Therefore the population recruited becomes slightly biased towards a preference for the intervention being investigated.
Is this important? Does it matter? I don’t know. Recent research by Wu et al suggests that women with a strong preference for vaginal birth were more likely to have a vaginal birth. RCTs cannot tell us the effect of women’s preferences on the outcomes they measure. Yet in theory their results are used to offer women an option they will almost certainly have an opinion about.
If I were contributing to the design of these trials, I would want to collect observational data alongside the main trial data. Things like:
- Why do women consent or decline to participate in the RCT? Are the women who declined to participate due to a strong preference against induction more or less likely to have a normal birth? Are the outcomes for their babies significantly different than those in either arm of the trial?
- What are the long-term outcomes? Especially in the over-35 population, an increase stillbirth rate may be due to inherent weaknesses in the baby. Significant long-term differences are often not detectable until 2 years of age.
- And finally .. would they do the again? Would they recommend it to a friend?
These are questions best answered using quantitative techniques, but women may have different questions or priorities, which we will only discover using qualitative investigations.
See Part 2: Why midwives are sceptical.