International guidelines recommend screening for overt diabetes in early pregnancy. Women in their first trimester with fasting plasma glucose (FPG) levels that would be diagnostic of gestational diabetes mellitus (GDM) in later pregnancy are being identified and treated despite uncertainty regarding the risks and benefits. The evidence for the current diagnostic criteria and management recommendations in early GDM are reviewed. The results of a prospective observational study assessing the progression to GDM and prespecified maternal‐fetal outcomes in women with mild fasting hyperglycaemia in the first trimester suggest that women with FPG 5.1–5.6 mmol/L may warrant proactive management in early pregnancy.