According to the National Institute of Diabetes and Digestive and Kidney Diseases:
People over age 45 should be tested for prediabetes or diabetes. If the first blood glucose test is normal, they should be retested every three years.
People under age 45 should consider getting tested for prediabetes or diabetes if they have a body mass index (BMI) of greater than or equal to 25 kgm/m2 and have one or more of the following risk factors:
Having a first-degree relative with diabetes (mother, father, or sibling)
Being a member of a high-risk ethnic group (African-American, Hispanic, Asian, Pacific Islander, or Native American)
Delivering a baby weighing more than 9 pounds, or having diabetes during pregnancy
Having blood pressure at or above 140/90 mm/Hg
Having abnormal blood fat levels, such as high-density lipoproteins (HDL) less than or equal to 35 mg/dL, or triglycerides greater than or equal to 250 mg/dL (mg/dL = milligrams of glucose per deciliter of blood)
Having a sedentary lifestyle
Having impaired glucose tolerance when previously tested for diabetes
Having polycystic ovarian syndrome
A diagnosis of diabetes is made when any one of these tests is positive. The result may be confirmed by a second positive test on a different day:
A1C greater than or equal to 6.5 percent
Fasting plasma glucose of greater than or equal to 126 mg/dL
Casual plasma glucose (taken at any time of the day) of greater than or equal to 200 mg/dL with the symptoms of diabetes
Oral glucose tolerance test (OGTT) value of greater than or equal to 200 mg/dL. The OGTT is obtained two hours after a drink containing glucose has been consumed, which occurs after fasting for at least eight hours.
Gestational diabetes may be diagnosed with one of two approaches:
A 75-gram glucose screening test, which involves drinking a glucose drink followed by measurement of the blood sugar level after two hours. This test is done at 24 to 28 weeks gestation.
A 50-gram glucose screening test, which is followed by a diagnostic 100-gram glucose tolerance test in those women whose blood sugar equals or exceeds 130 mg/dL one hour after the initial screening test
Consult your doctor regarding your wish to be screened for gestational diabetes.