Diabetes mellitus is a group of metabolic diseases characterized by hyperglycemia due to defects in insulin secretion or action. The chronic hyperglycemia can lead to long-term damage in various organs, particularly the eyes, kidneys, nerves, heart, and blood vessels. Diabetes can be caused by autoimmune destruction of β-cells in the pancreas, resulting in insulin deficiency, or by abnormalities that lead to insulin resistance. Type 1 diabetes, accounting for 5-10% of cases, is characterized by absolute insulin deficiency, often with autoimmune destruction of β-cells. Type 2 diabetes, the more common form (90-95% of cases), involves insulin resistance and relative insulin deficiency. Other types include genetic defects in β-cell function, insulin action, and exocrine pancreas diseases. Gestational diabetes mellitus (GDM) is diagnosed during pregnancy and can persist postpartum, leading to type 2 diabetes. The diagnosis of diabetes is based on fasting plasma glucose, 2-hour plasma glucose after an oral glucose load, or A1C levels. New diagnostic criteria for GDM have been established to improve detection and management.Diabetes mellitus is a group of metabolic diseases characterized by hyperglycemia due to defects in insulin secretion or action. The chronic hyperglycemia can lead to long-term damage in various organs, particularly the eyes, kidneys, nerves, heart, and blood vessels. Diabetes can be caused by autoimmune destruction of β-cells in the pancreas, resulting in insulin deficiency, or by abnormalities that lead to insulin resistance. Type 1 diabetes, accounting for 5-10% of cases, is characterized by absolute insulin deficiency, often with autoimmune destruction of β-cells. Type 2 diabetes, the more common form (90-95% of cases), involves insulin resistance and relative insulin deficiency. Other types include genetic defects in β-cell function, insulin action, and exocrine pancreas diseases. Gestational diabetes mellitus (GDM) is diagnosed during pregnancy and can persist postpartum, leading to type 2 diabetes. The diagnosis of diabetes is based on fasting plasma glucose, 2-hour plasma glucose after an oral glucose load, or A1C levels. New diagnostic criteria for GDM have been established to improve detection and management.