Rates of gestational diabetes mellitus (GDM) and Type 2 diabetes in pregnancy are increasing with the epidemic of obesity. GDM is associated with significant perinatal morbidity and future risk of permanent diabetes in the mother and obesity and diabetes in the offspring. The recent Australian Carbohydrate Intolerance Study in Pregnant Women (ACHOIS) has shown maternal and perinatal benefits of managing GDM once diagnosed. The criteria for GDM are under review following the recent completion of the Hyperglycaemia and Adverse Perinatal Outcomes study (HAPO). In New Zealand, the approach to identifying women with GDM or undiagnosed Type 2 diabetes has varied. The National GDM Technical Working Party reviewed the available data in the New Zealand context and recommend that (1) All pregnant women are offered screening for GDM backed up with relevant educational, systems and materials for health professionals and the women; (2) Criteria for GDM should remain unchanged pending further information (which should be actively sought); (3) Women at high risk of undiagnosed Type 2 diabetes in pregnancy should be screened at booking: the HbA1c was recommended as a practical initial screening test, but further research is needed; and (4) A structured, audited, population-based approach to managing women with GDM should be introduced in each district.