Retrospective audit of prospectively collected data for all patients with gestational diabetes mellitus from 1993 to 2010. We defined overt diabetes in pregnancy as an HbA(1c) ≥ 8 mmol/mol (6.5%) or a fasting plasma glucose ≥ 7.0 mmol/l, or a 2-h glucose level ≥ 11.1 mmo/L on a 75-g oral glucose tolerance test as a surrogate for a random glucose ≥ 11.1 mmo/l.