Gestational diabetes mellitus (GDM) is defined as glucose intolerance of any degree with onset or first recognition during pregnancy. In Singapore, 20-30% of pregnant women are affected by GDM. If poorly controlled, GDM is associated with various maternal and perinatal morbidities such as increased cesarean deliveries, preeclampsia, preterm labour, macrosomia, neonatal hypoglycemia etc. It is well recognized now that GDM is also associated with long-term metabolic complications in mothers and offspring. Women with a history of GDM have increased risk of GDM in subsequent pregnancies, and at high risk of developing Type 2 diabetes after pregnancy. Infants born to mothers with GDM are also at increased risk of developing obesity and diabetes in later life. An increasing number of studies, including studies in Singapore, suggest that screening and management of GDM can be cost-effective, although these results are highly dependent on intervention efficacy.