In this study, during the past 20-30 years, the prevalence of diabetes mellitus (DM) has rapidly increased throughout the world. The prediction being that it will increase by 200% in the next several decades. Pregnancy may precipitate diabetes in previously healthy but susceptible individuals. Diabetes raises the risk of a complicated pregnancy, increasing both maternal and perinatal mortality, and the risk of congenital malformations. Pregnancy may cause deterioration of established diabetic complications and should be avoided in those with poor glycaemic control. Tight control of diabetes during pregnancy reduces adverse outcomes substantially. Most patients with pre-existing diabetes will require insulin during pregnancy to achieve optimal targets if they are not already using it. Management should be coordinated through close liaison and frequent review by the diabetes, obstetric and midwifery teams.