Gestational diabetes (GDM) develops during pregnancy and is becoming increasingly common. The condition is associated with adverse outcomes for mother and baby during both the pregnancy and delivery period. This study compares glucose variability (recorded by a continuous glucose monitoring (CGM) sensor) in pregnant women who have been diagnosed with GDM with pregnant woman who do not have the diagnosis but are at high risk. The sensors will be applied to 400 participants around the time of their standard test for GDM, with a randomly selected 60 of these patients forming a sub-group later in the study to assess for progression of high blood glucose. At present, a positive oral glucose tolerance test (OGTT) is used to confirm the diagnosis of GDM but the test can be unreliable leading to potential diagnostic error. CGM devices are used extensively in the management of Type 1 diabetes and GDM, and have also shown potential to be used in the diagnosis of Type 2 diabetes. If this study can demonstrate similar trends in glucose variability between OGTT positive patients and those who are OGTT negative but are at high risk for the condition, then further research into the utility of CGM as a diagnostic alternative or supplement to the OGTT would be indicated. The investigators will recruit 400 patients at high risk for GDM, give them a blinded CGM device, and compare the CGM glucose data with their OGTT result, their initial risk factors for GDM, their pregnancy outcome and their need for treatment. The investigators will use the data to test our hypothesis that a positive OGTT result does not predict hyperglycaemia in pregnancy.