An estimated 34 million adults are living with diabetes in the United States, and of those, 14.9 million are women. The prevalence of diabetes mellitus in women of reproductive age is estimated at 3.1%-6.8%.

Type 1 diabetes is caused by insulin deficiency following autoimmune T-cell mediated destruction of pancreatic beta cells. It is typically diagnosed in childhood, but it accounts for a quarter of new diabetes cases in adults. These patients become insulin dependent. Risk factors include having a close relative with type 1 diabetes and non-Hispanic White or Black race / ethnicity.

Type 2 diabetes is typically diagnosed in adults and is related to obesity and peripheral insulin resistance. While obesity is the biggest risk factor for type 2 diabetes, genetics also plays a strong role. Type 2 diabetes is the most common form of pregestational diabetes.

Type 1 and type 2 diabetes incidence has increased in recent years, in part due to increasing obesity in the United States. Incidence varies by race and ethnicity. Some studies suggest that non-Hispanic White and Asian individuals have lower rates of diabetes. Native American individuals have a higher rate of type 2 diabetes.

Certain exposures may increase the risk of type 2 diabetes. These include:

• Chronic exposure to arsenic in drinking water.
• Exposure to bisphenol A, which is found in hard plastics.
• Chronic exposure to pesticides.

Pregestational diabetes is observed in 1%-2% of pregnancies. Not all women with preexisting diabetes mellitus will show classic symptoms, making preventive care an important component of diagnosis when associated with pregnancy.

The diagnosis of pregestational diabetes is easily made preconception, in the first trimester, or in the early second trimester. There is no consensus on diagnosis in the late second trimester or third trimester, due to inability to distinguish from gestational diabetes at that time.