Alternatively, a more involved diagnostic test can be used directly at the first prenatal visit for a woman with a high-risk pregnancy. (for example in those with polycystic ovarian syndrome or acanthosis nigricans).Non-challenge blood glucose tests involve measuring glucose levels in blood samples without challenging the subject with glucose solutions. A blood glucose level is determined when fasting, two hours after a meal, or simply at any random time. In contrast, challenge tests involve drinking a glucose solution and measuring glucose concentration thereafter in the blood; in diabetes, they tend to remain high. The glucose solution has a very sweet taste which some women find unpleasant; sometimes, therefore, artificial flavours are added. Some women may experience nausea during the test, and more so with higher glucose levels.There is currently not enough research to show which way is best at diagnosing gestational diabetes. Routine screening of women with a glucose challenge test may find more women with gestational diabetes than only screening women with risk factors. It is not clear how these screening tests affect the rest of the pregnancy. Future research should include how the method of screening impacts the mother and baby. Pathways
Opinions differ about optimal screening and diagnostic measures, in part due to differences in population risks, cost-effectiveness considerations, and lack of an evidence base to support large national screening programs.
Type T: prior kidney transplant.An early age of onset or long-standing disease comes with greater risks, hence the first three subtypes.Two other sets of criteria are available for diagnosis of gestational diabetes, both based on blood-sugar levels.Criteria for diagnosis of gestational diabetes, using the 100 gram Glucose Tolerance Test, according to Carpenter and Coustan:
Fasting 95 mg/dl
1 hour 180 mg/dl
2 hours 155 mg/dl
3 hours 140 mg/dlCriteria for diagnosis of gestational diabetes according to National Diabetes Data Group:
Fasting 105 mg/dl
1 hour 190 mg/dl
2 hours 165 mg/dl
3 hours 145 mg/dl

Risk factors
Classical risk factors for developing gestational diabetes are:
Polycystic ovary syndrome
A previous diagnosis of gestational diabetes or prediabetes, impaired glucose tolerance, or impaired fasting glycaemia
A family history revealing a first-degree relative with type 2 diabetes
Maternal age – a womans risk factor increases as she gets older (especially for women over 35 years of age). Paternal age – one study found that a fathers age over 55 years was associated with GD
Ethnicity (those with higher risk factors include African-Americans, Afro-Caribbeans, Native Americans, Hispanics, Pacific Islanders, and people originating from South Asia)
Being overweight, obese or severely obese increases the risk by a factor 2.1, 3.6 and 8.6, respectively. A previous pregnancy which resulted in a child with a macrosomia (high birth weight: >90th centile or >4000 g (8 lbs 12.8 oz))
Previous poor obstetric history
Other genetic risk factors: There are at least 10 genes where certain polymorphism are associated with an increased risk of gestational diabetes, most notably TCF7L2.In addition to this, statistics show a double risk of GDM in smokers.