High prevalence and significant ethnic differences in actionable HbA(1C) after gestational diabetes mellitus in women living in Norway

BACKGROUND: The type 2 diabetes risk after gestational diabetes mellitus (GDM) is twice as high in South Asian compared to European women. Current guidelines differ regarding which test to use as a screening-tool post-GDM. We aimed to identify ethnic differences in the prevalence rates and early predictors for actionable HbA(1c) (defined as prediabetes and diabetes) short time after GDM. METHODS: This cross-sectional study, enrolling South Asian and Nordic women 1–3 years after a diagnosis of GDM, was undertaken at three hospitals in Norway. We performed a clinical and laboratory evaluation including an oral glucose tolerance test (OGTT). Medical records were used to retrieve data during pregnancy. Prediabetes was classified with HbA(1c) alone or combined with OGTT glucose measurements according to the WHO, WHO-IEC, and ADA criteria (fasting plasma glucose (FPG) 6.1–6.9 mmol/L, FPG 6.1–6.9 mmol/L and/or HbA(1c) 42-47 mmol/mol (6.0-6.4%), and FPG 5.6–6.9 mmol/L and/or HbA(1c) 39-47 mmol/mol (5.7-6.4%)). Ethnic differences in prevalence and predictors of glucose deterioration were assed by χ(2) (Pearson) tests and logistic regression models. RESULTS: We included 163 South Asian and 108 Nordic women. Actionable HbA(1c) levels were highly prevalent and more so among South Asian than Nordic women (WHO-IEC-HbA(1c): 25.8% vs. 6.5% (p ≤ 0.001), ADA-HbA(1c): 58.3% vs. 22.2% (p ≤ 0.001)). Although adding OGTT-data gave higher combined prevalence rates of prediabetes and diabetes (WHO: 65.6% vs. 47.2% (p ≤ 0.05), WHO-IEC: 70.6% vs. 47.2% (p ≤ 0.001), ADA: 87.8% vs. 65.7% (p ≤ 0.001)), the excess risk in the South Asian women was best captured by the HbA(1c). Important predictors for glucose deterioration after GDM were: South Asian ethnicity, GDM before the index pregnancy, use of glucose-lowering drugs in pregnancy, higher age, and higher in-pregnancy fasting glucose levels. CONCLUSIONS: In women with GDM 1–3 year previously, we found high prevalence and significant ethnic differences in actionable ADA-HbA(1c) levels, with South Asian ethnicity, GDM before the index pregnancy, and the use of glucose-lowering drugs in pregnancy as the most important risk factors. This study reinforces the importance of annual screening—preferably with HbA(1c) measurements—to facilitate early intervention after GDM. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12916-022-02515-w.