Birth Small Talk

Talking about birth

Customised growth charts and stillbirth prevention: New research

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Reducing the rate of stillbirth continues (quite appropriately) to be a central priority for maternity services and clinicians. In addition to CTG monitoring, fetal growth assessment is a key technological tool used as a means to prevent stillbirth. I have previously described the assumptions made in the fetal distress meta-narrative, which is the logic on which CTG monitoring is based. A similar meta-narrative, which I’m going to call the fetal growth meta-narrative, forms the logic for the use of fetal growth monitoring as a means to prevent stillbirth.

What does that mean exactly? A meta-narrative is a set of beliefs which structures our thinking. In the case of both the fetal distress and the fetal growth meta-narratives there are elements that are backed up by research and others which are not, but seem to be a logical idea. The fetal growth meta-narrative goes something like this:

  • We believe that many / most instances of stillbirth are preventable and that preventing stillbirth is an important goal.
  • We have developed statistical measures of fetal size in order to have a shared professional language – with the most commonly used approach being to describe the size of the fetus against population-based centiles. 
  • Fetuses who are in the lower range of centiles have been shown to experience stillbirth more often than those in the mid-range of centiles. 
  • The logical assumption that flows from this is that if we detect all small fetuses and plan to achieve their birth before they die, then the problem of stillbirth will largely be solved.

This was the assumption underpinning the Growth Assessment Protocol or GAP program. The GAP program trains clinicians to reliably measure symphysio-fundal height (the distance between the top of the woman’s uterus and the top of her pubic bone) as an indicator of fetal size and to plot this on a centile chart which has been customised according to the woman’s specific characteristics (age, height, weight, previous births, ethnicity). It has been claimed that the GAP program reduces stillbirth, but research evidence to back this up has been on the slim side. 

Iliodromiti and colleagues (2020) took up the challenge of trying to answer this tricky question. These researchers compared the rate of change in stillbirth between 2000 and 2015 in England and Wales (countries where the GAP program has been widely introduced), with Scotland (where the program was implemented much later). Maternity services in these countries are provided by the NHS and therefore share many similarities. Prior to 2015 only 7% of Scottish maternity services were using the GAP program, compared to 68% in England and Wales. This provides a sort of natural experiment, were outcomes can be compared to see what is going on.

Looking at their results, the stillbirth rates in England and Wales were static until 2010 (at a rate of around five stillbirths per 1000 births), then began to fall slightly, ending at 4.3 per 1000 births in 2015. Scotland showed a similar pattern, with stillbirth rates of around five per 1000 births, then a fall after 2010, but to a lower end point in 2015 of 3.75 per 1000 births. The decline in stillbirth in Scotland was faster (achieving statistical significance) after 2010 than it was in England and Wales. 

In summary, while there was a fall in stillbirth rate in the later years of the study in all areas, the reduction was highest in Scotland where the use of the GAP program was lowest. The authors explored possible reasons for these findings, noting that Scotland has been more successful in reducing rates of smoking and increasing the uptake of antenatal care in the first trimester. The authors also point out that the assumption that we should adjust growth charts for variations in ethnicity and weight and so on might be wrong, and that doing so means that some fetuses might not recognised as small on the customised chart but are still at higher risk. 

Where does that leave us then? There is an increasing focus on the introduction of “bundles” of care (most recently focussed on stillbirth prevention and the prevention of severe perineal trauma) where some sound evidence is mixed with a few good ideas, and some reasonable sounding assumptions. These bundles are then rolled out in a large-scale manner, sometimes in ways that would not be considered ethical if they were a research project, and not always with a sound evaluation plan in place to determine whether they work or generate new harms. Maternity clinicians need to retain their critical thinking skills, challenge the hype and the buzz, and continue to provide individualised rather than standardised care. In this instance it seems that there are gaps in the GAP program.  

Iliodromiti, S., Smith, G. C. S., Lawlor, D. A., Pell, J. P., & Nelson, S. M. (2020, May). UK stillbirth trends in over 11 million births provide no evidence to support effectiveness of Growth Assessment Protocol program. Ultrasound Obstet Gynecol, 55(5), 599-604.

Categories: New research, Stillbirth

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