Diabetes Mellitus Incidence and Classification

Study Notes

The prevalence of diabetes mellitus has increased significantly over the last 20 years.
In the United States, the rates of diabetes range from 6-12% depending on the population and diagnostic criteria.
80-90% of diabetes in pregnant women is gestational, and 10% is pregestational.
Gestational diabetes mellitus (GDM) is defined as glucose intolerance with onset or first recognition during pregnancy.
Rising levels of human placental lactogen, progesterone, prolactin, and cortisol in pregnancy contribute to progressive insulin resistance.
Women who develop GDM have chronic insulin resistance, and GDM is a "stress test" for the development of diabetes later in life.

Pregestational diabetes mellitus refers to diabetes present before pregnancy and may be either type 1 or type 2 diabetes.
The White classification is used to further refine the categories for GDM and pregestational diabetes.
This classification is helpful for assessing disease severity and the likelihood of complications.

Maternal and fetal complications of diabetes include risks associated with the metabolic syndrome (central obesity, insulin resistance, and hyperlipidemia).
Most fetal and neonatal effects are attributed to maternal hyperglycemia or maternal vascular disease.
Glucose crosses the placenta easily, causing fetal hyperglycemia, which stimulates pancreatic β-cells and results in fetal hyperinsulinism.
Fetal hyperglycemia during embryogenesis is teratogenic and correlates with birth defects and increasing glycosylated hemoglobin A1C (HbA1C) levels in the first trimester.

Fetal hyperglycemia and hyperinsulinemia later in pregnancy cause fetal overgrowth and macrosomia, predisposing to birth trauma, including shoulder dystocia and Erb palsy.
Fetal demise is due to acidosis, hypotension from osmotic diuresis, or hypoxia from increased metabolism, coupled with inadequate placental oxygen transfer.

Pregestational diabetes is associated with a higher rate of maternal and fetal complications due to difficulty in achieving glycemic control, higher rates of congenital malformations, and vascular disease.
Maternal complications include worsening nephropathy and retinopathy, preterm preeclampsia, and a higher likelihood of diabetic ketoacidosis.
Fetal complications include an increased rate of abortions, anatomic birth defects, fetal growth restriction, and prematurity.

The American College of Obstetricians and Gynecologists (ACOG) recommends a two-step method to test for GDM.
The first step involves universal screening for gestational diabetes between 24 and 28 weeks' gestation with a 50-g, 1-hour oral glucose challenge test (OGCT).
Screening is advised at the first prenatal visit in women with risk factors such as a previous pregnancy with GDM, history of polycystic ovarian disease, or obesity.