Inclusion Criteria:  -  Age ≥ 18yrs, and at least one of the following NICE risk factors for glucose intolerance:  body mass index ≥ 30kg/m2 a family history of diabetes (first-degree relative) previous macrosomic baby (>4.5kg) minority ethnic family origin with a high prevalence of diabetes  Exclusion Criteria:  - pre-existing type 1 or type 2 diabetes mellitus, a previous history of GDM, booking HbA1c ≥ 48mmol/mol (6.5%), anaemia diagnosed on booking full blood count, booking diagnosis of a multiple pregnancy, use of corticosteroids or metformin within 12 weeks of booking