In 1997, the American Diabetes Association (ADA) revised the classification of diabetes. The new designations are based upon the cause, not treatment, for each class of diabetes. Where numbers are used for type classification, Arabic numerals have replaced Roman numerals for greater clarity and ease. The ADA classified diabetes into four main types:
- Type 1 diabetes: Due to β-cell destruction, usually leading to absolute insulin deficiency
- Type 2 diabetes: Due to a progressive insulin secretory defect on the background of insulin resistance
- Gestational diabetes mellitus (GDM): Diabetes diagnosed in the second or third trimester of pregnancy that is not clearly overt diabetes
- Specific types of diabetes due to other causes: Examples include monogenic diabetes syndromes (eg, neonatal diabetes and maturity-onset diabetes of the young), diseases of the exocrine pancreas (eg, cystic fibrosis), and drug- or chemical-induced diabetes (eg, treatment of HIV/AIDS or after organ transplantation).