The diagnosis of gestational diabetes has for decades been based either on criteria that predict a mother’s risk for developing type 2 diabetes in the future, or those used for non-pregnant women. But gestational diabetes also carries a risk for the baby. Moreover, the level at which maternal blood glucose provokes risk for the foetus remains unclear. Expert opinions on screening for gestational diabetes are divided: while some believe that mild hyperglycaemia increases the risk to the baby’s health, others assert that such mild elevations of blood glucose have no adverse effects, and that systematic efforts to diagnose gestational diabetes should be stopped. The HAPO Study was designed to address the question as to whether the risk of an adverse outcome for the baby can be related to degrees of maternal glucose intolerance below the established cut-off points for diabetes. This article provides information on some of the initial findings and the potential for their application in clinical practice internationally.