Irisin is a newly described myokine that improves insulin resistance via the browning of white adipose tissue. Irisin appears to be secreted in response to exercise, providing a hormonal link between exercise and improved insulin sensitivity. Irisin expression has been demonstrated to increase after acute exercise and cold exposure in animal and human studies. Circulating irisin is decreased in metabolic disease states characterised by insulin resistance, such as type 2 diabetes mellitus, non-alcoholic fatty liver disease, chronic kidney disease and metabolic syndrome. The role of irisin in in normal pregnancy as well as gestational diabetes mellitus is yet to be fully elucidated. To date, there are inconsistent reports regarding the changes in circulating irisin that occur in pregnancy and Gestational Diabetes Mellitus (GDM). Overall, it appears that irisin levels increase with pregnancy, and that the placenta expresses low levels of irisin. There is evidence that irisin levels are decreased in GDM pregnancy. With further research, irisin may prove a future therapeutic target or risk marker for GDM as well as other disease states characterised by insulin resistance.