High prevalence and significant ethnic differences in actionable HbA_1C after gestational diabetes mellitus in women living in Norway.

Abstract

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. 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 χ² (Pearson) tests and logistic regression models. 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. 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.