Gestational Diabetes Mellitus and Risk Factors in a Multi‐Ethnic National Case–Control Study

ABSTRACT Introduction Gestational diabetes mellitus (GDM) continues to increase particularly for non‐European women. This study aimed to identify and quantify risk factors for women diagnosed with gestational diabetes in New Zealand to identify women at higher risk. Methods A national dataset of 601,166 eligible women who had ≥ 1 birth in New Zealand between January 2001 and December 2010 identified 11,459 women with gestational diabetes of whom 11,447 were randomly matched with 57,235 control women for age and year of delivery. Results Adjusted odds ratios (95% CI) showed higher odds of gestational diabetes for Asian (3.60, 3.39–3.82), Pacific (2.76, 2.57–2.96) and Māori (1.23, 1.15–1.31) women compared with European/Other women. Women most economically disadvantaged (1.44, 1.34–1.56), not registered with a lead maternity carer (1.16, 1.04–1.30) and those identified as smokers (1.20, 1.11–1.31) were more likely than control women to develop gestational diabetes. In contrast, women residing in rural (0.83, 0.77–0.88) and remote areas (0.68, 0.60–0.77) were less likely to develop gestational diabetes compared with women living in urban areas, and similarly for non‐New Zealand resident women (0.78, 0.72–0.85) compared with resident women. Conclusions Women who were diagnosed with gestational diabetes were more likely to be non‐European, economically disadvantaged, residing in urban areas, unregistered with a lead maternity carer and more likely to smoke. In addition to universal screening for pre‐existing diabetes, all women at risk of gestational diabetes should be identified and supported to undertake to a 75 g glucose challenge test between 24 and 28 weeks.