Should GDM screening come sooner in pregnancy?

3 minute read

An international consortium has called for earlier testing and treatment, but not all are convinced.

Earlier gestational diabetes screening: yay or nay? 

Gestational diabetes mellitus (GDM) is the most common medical complication in pregnancy, affecting 14% of pregnancies worldwide, and has historically been tested for and treated in the second or third trimester. 

But a new series of papers has called for testing and treatment to start much earlier in pregnancy – before the 14-week mark – claiming the move can prevent complications and improve long-term outcomes for both mother and child.  

The three papers, which cover the pathophysiology, epidemiology and management of GDM, were published in The Lancet.  

“The benefits of early GDM detection are clear – we can keep mothers and babies healthier during pregnancy and hopefully continue that path for a lifetime. What is needed now is earlier testing and an approach to managing GDM that takes the available resources, circumstances and personal wishes of the patient into consideration,” said co-author Dr Helena Backman (Örebro University, Sweden). 

The International Diabetes Federation reports 30-70% of GDM cases experience hyperglycaemia at or before 20 weeks. Estimates of the prevalence of GDM in women screened before 12 and 20 weeks have a wide range – from 1-14% and 1-37%, respectively – depending on the population and specific diagnostic methods/criteria used.  

A pair of systematic reviews (published in 2017 and 2022) suggest women diagnosed with early gestational diabetes have worse outcomes than women diagnosed between 24 and 28 weeks of gestation: higher rates and greater risk of perinatal mortality, neonatal morbidity and congenital anomalies.  

Research such as the Australian-lead Treatment of Booking Gestational Diabetes Mellitus (TOBOGM) study, published in the New England Journal of Medicine, has also shown the identification and treatment of GDM before 20 weeks led to modest reductions in adverse neonatal outcomes compared with deferring treatment until after the results of an oral glucose tolerance test were obtained at 24-28 weeks.  

On the other hand, an accompanying editorial felt the modest benefits observed in the TOBOGM trial, along with the results of another recent trial showing early screening was not associated with a reduction in mortality, made the need for earlier screening questionable.  

Distinguished Professor David Simmons, an endocrinologist from Western Sydney University and one of the lead authors of the series, told The Medical Republic that the benefits of moving the oral glucose tolerance testing to an earlier stage of pregnancy would outweigh any potential drawbacks for women and health services. 

“It is past time to move from ‘late pregnancy’ focused services to an integrated, personalised life-course strategy across both high- and low-resource settings,” Professor Simmons said in a statement.  

“This includes new, systematic approaches to prevention, early GDM treatment, identifying and overcoming barriers to uptake, better health system integration, and more research to better understand how GDM affects women and their children during pregnancy and throughout their lives.” 

Professor Simmons told TMR that the Australasian Diabetes in Pregnancy Society, of which he is president, was preparing a new set of guidelines together with the RACGP, RANZCOG and the Australian Medical Council, which would hopefully be released in late July or early August.  

But Dr Gary Deed, chair of the RACGP’s diabetes specific interest group, said that while the call for expanded testing and treatment sounded wonderful in theory, there was still uncertainty regarding the benefits of earlier testing, how high-risk populations would be defined and whether different cutoffs or definitions would be used in earlier screening.  

The Lancet 2024, online 20 June 

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