Diabetes mellitus (DM) classification by etiology
- Type 1 (previously called insulin-dependent DM or juvenile-onset DM)
- Type 2 (previously called non-insulin-dependent DM or adult-onset DM)
- Gestational diabetes (diabetes diagnosed in pregnancy)
Type 1 DM accounts for approximately 5-10% of patients and is generally due to autoimmune destruction of the pancreatic beta-cells, leading to absolute insulin deficiency. Although typically diagnosed in patients before age 30, it can present at any age due to variability in the rate of beta-cell destruction.
The majority of patients have type 2 DM, which is associated with insulin resistance and relative insulin deficiency. Most patients are obese (predominantly abdominal accumulation). Type 2 DM is diagnosed in adulthood, and patients are not prone to develop ketoacidosis except in association with the stress from another illness.
Gestational DM, which is diagnosed during pregnancy, occurs in approximately 4% of pregnant women and usually presents in the second or third trimester when insulin resistance normally occurs. It is associated with increased fetal morbidity and mortality. Glucose tolerance usually returns to normal after delivery, but 30-40% of women with gestational DM develop type 2 DM within 10 years.