These two groups are further subdivided according to their associated risks and management.The two subtypes of gestational diabetes under this classification system are:

Type A1: abnormal oral glucose tolerance test (OGTT), but normal blood glucose levels during fasting and two hours after meals; diet modification is sufficient to control glucose levels
Type A2: abnormal OGTT compounded by abnormal glucose levels during fasting and/or after meals; additional therapy with insulin or other medications is requiredDiabetes which existed prior to pregnancy is also split up into several subtypes under this system:
Type B: onset at age 20 or older and duration of less than 10 years. Type C: onset at age 10–19 or duration of 10–19 years. Type D: onset before age 10 or duration greater than 20 years. Type E: overt diabetes mellitus with calcified pelvic vessels. Type F: diabetic nephropathy. Type R: proliferative retinopathy. Type RF: retinopathy and nephropathy. Type H: ischemic heart disease.
This test will identify fewer women who are at risk, and there is only a weak concordance (agreement rate) between this test and a three-hour 100 g test.The glucose values used to detect gestational diabetes were first determined by OSullivan and Mahan (1964) in a retrospective cohort study (using a 100 grams of glucose OGTT) designed to detect risk of developing type 2 diabetes in the future. The values were set using whole blood and required two values reaching or exceeding the value to be positive. Subsequent information led to alterations in OSullivans criteria. When methods for blood glucose determination changed from the use of whole blood to venous plasma samples, the criteria for GDM were also changed. Urinary glucose testing
Women with GDM may have high glucose levels in their urine (glucosuria). Although dipstick testing is widely practiced, it performs poorly, and discontinuing routine dipstick testing has not been shown to cause underdiagnosis where universal screening is performed. Increased glomerular filtration rates during pregnancy contribute to some 50% of women having glucose in their urine on dipstick tests at some point during their pregnancy. The sensitivity of glucosuria for GDM in the first two trimesters is only around 10% and the positive predictive value is around 20%. Prevention
Vitamin D supplementation during pregnancy may help to prevent gestational diabetes. A 2015 review found that when done during pregnancy moderate physical exercise is effective for the prevention of gestational diabetes. A 2014 review however did not find a significant effect.