Universal Screening with a Glucose Challenge Test to Predict Gestational Diabetes Mellitus in a Diverse Population: A Retrospective Cohort Study
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Introduction
Gestational diabetes mellitus (GDM) is associated with significant maternal and neonatal morbidity. Screening strategies vary internationally and the diagnostic performance of the 50g glucose challenge test (50g GCT) as a universal screening tool remains uncertain across diverse populations.
Research design and methods
This retrospective cohort study included 18,213 singleton pregnancies at a London tertiary hospital between 2010 and 2023. Women routinely underwent the universal two-step GDM screening pathway: a 50g GCT at 24–32 weeks’ gestation, followed by a diagnostic 75-g oral glucose tolerance test if the 50g GCT result was ≥7.8 mmol/L. We evaluated the use of universal two-step screening in detecting GDM, how its prevalence varies with maternal characteristics, including ethnicity, body mass index, age, and in those who would not have been included in risk factor-indicated screening, and the association between the 50g GCT and adverse outcomes.
Results
2,015 women had an abnormal GCT, and 406 (20.1%) had an abnormal 75g OGTT, with GDM diagnosed at 24-28 weeks. We also found 87 women, despite a normal GCT and/or normal OGTT, developed late-onset GDM. The overall prevalence of GDM was 4.4% (810/18,213). Universal screening will therefore identify a significant number of GDM cases, notably including those in a low-risk cohort who would not have been screened using a risk factor-based approach. When we examined glucose as a continuous variable, there was an association between increasing 50g GCT values and adverse maternal and neonatal outcomes.
Conclusion
Universal screening with a GCT is a feasible and safe approach and addresses a significant health disparity gap, in that women without risk factors are screened and may be diagnosed with GDM. Given the long-term cardiometabolic implications of GDM, pregnancy diagnosis is important to allow for longer-term targeting of cardiometabolic risk factors to improve long-term health screening for type 2 diabetes and obesity.
Key messages
What is already known on this topic
Gestational diabetes mellitus (GDM) is associated with maternal and neonatal morbidity, which is substantially reduced with early recognition and management.
GDM screening approaches vary substantially in efficiency, diagnostic accuracy, and resource use. Universal screening with a 75g oral glucose tolerance test (75g OGTT) is resource-intensive, yet risk factor-based screening alone risks missing GDM in women without recognised risk factors.
The recurrence risk of GDM is up to 41.3%, and women with GDM are more likely to develop type 2 diabetes and cardiovascular disorders; therefore, diagnosis of GDM is important to identify and intervene in those women who are at higher risk.
GDM is associated with increased offspring adiposity and childhood obesity, impaired glucose metabolism and a substantially elevated long-term risk of prediabetes and type 2 diabetes, as well as a broader adverse cardiometabolic profile.
What this study adds
Universal screening detected GDM in women who may not have been offered screening based on risk factors.
Around 1/3 of GDM cases detected in this population were diagnosed later in pregnancy following negative GCT and/or negative OGTT.
The relationship between maternal glycaemia and adverse pregnancy outcomes is continuous across GCT glucose levels, with risk increasing with increased glucose levels.
How this study might affect research, practice or policy
Further research is needed to investigate how a universal screening approach in diagnosing GDM addresses longer-term cardiometabolic health.
Variation in the predictive value of a GCT for GDM by maternal characteristics should be considered when evaluating and optimising any universal screening strategy.
A GCT population could form part of a hybrid GDM screening strategy where high-risk women proceed directly to 75g OGTT and women considered at low risk of GDM benefit from screening by GCT.
