According to the National Institute for Health and Care Excellence (NICE) around 700 000 women give birth in England and Wales annually; up to 5% of these women have either pre-existing diabetes or gestational diabetes mellitus (GDM); and the incidence of GDM is rising because of higher obesity rates in the general population and more pregnancies in older women (NICE, 2015).
In a UK study, Barker et al (2017) identified 3 033 women with GDM, reporting that the strongest risk factor for GDM was obesity, and that other significant risk factors included Asian ethnicity, previous GDM and pharmacological treatment for GDM; Sukumar et al (2016) conducted the first UK study to show that maternal blood vitamin B12 concentrations are associated with body mass index, risk of GDM and may have an independent effect on macrosomia; and Stacey et al (2019) reported that optimal screening and diagnosis of GDM mitigate ‘the higher risks of late stillbirth in women “at risk” of GDM and/or with raised fasting plasma glucose (FPG). Failure to diagnose GDM leaves women with raised FPG exposed to avoidable risk of late stillbirth.’
NICE (2015) advises selected screening for those women with any 1 of 5 designated risk factors – including previous GDM and family history of diabetes – with GDM diagnosed ‘if the woman has either: a FPG level of 5.6 mmol/litre or above or a two-hour plasma glucose level of 7.8 mmol/litre or above.’
From the foregoing, it seems clear that it is important to identify those women with GDM or at risk of contracting the condition. However, the debate around GDM raises issues that are more complex than they might at first appear. For example, Farrar and Sheldon (2019) comment on the findings of Stacey et al (2019) that women at risk of GDM who received oral glucose tolerance testing had a lower risk of stillbirth than women with a risk factor who were not tested. According to Farrar and Sheldon (2019): ‘This does not, however, mean that routine screening for GDM is sufficiently clinically effective to justify the resources needed to implement it. The study is likely to be confounded by socioeconomic status…’ with higher stillbirth rates found among the most deprived.
Ethical aspects of GDM research have also arisen. For example, in a randomised controlled trial of treatment for mild GDM, Landon et al (2010) found that treatment significantly reduced ‘the risks of fetal overgrowth, shoulder dystocia, caesarean delivery and hypertensive disorders.’ However, Landon et al (2009) withheld from 455 women in the control group (and their caregivers) the results of their oral glucose-tolerance tests. Bloomgarden (2010) highlights the suggestion that by doing so, Landon et al (2009) subjected 455 women and 455 fetuses to ‘adverse effects … known by the investigators to be likely to lead to adverse outcome, and calls attention to … the non-disclosure of test results, and to the importance of non-financial conflicts of interest …’ It is a view that Landon et al (2010) challenge.
Meanwhile, Edwell and Jack (2017) draw attention to the difficulty of defining GDM and establishing the optimum screening protocol: ‘While experts generally agree that GDM poses risks to both pregnant mothers and the fetus, they disagree about the threshold for diagnosing it: at what point does a woman's glycaemic level adversely affect a pregnancy?’
Edwell and Jack (2017) note the disagreements between researchers both about the best evidence-based testing protocols and the glucose concentrations that indicate GDM. Faced with such uncertainty, say Edwell and Jack (2017), scientists typically promote trust in the scientific method, hoping it might ultimately produce a consensus: ‘Rather than simply positioning the latest guidelines as the natural outcome of years of past study, researchers tend to tell a story of continued uncertainty.’ Edwell and Jack (2017) argue that such deferment of the debate while further research is awaited promotes a breakdown in trust between patients, practitioners and scientists. Further, given that many patients undertake their own research and are aware of scientific disagreements, ‘[p]ractitioners might better address this problem by openly acknowledging that different diagnostic standards exist and explaining why they adhere to a particular approach’ (Edwell and Jack, 2017).
The GDM debate is one that midwives might expect to be drawn into by concerned patients whose access to peer-reviewed studies make them increasingly well-informed about the nuances of scientific discourse.