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.
The most elaborate regimen entails a random blood glucose test during a booking visit, a screening glucose challenge test around 24–28 weeks gestation, followed by an OGTT if the tests are outside normal limits. If there is a high suspicion, a woman may be tested earlier.In the United States, most obstetricians prefer universal screening with a screening glucose challenge test. In the United Kingdom, obstetric units often rely on risk factors and a random blood glucose test. The American Diabetes Association and the Society of Obstetricians and Gynaecologists of Canada recommend routine screening unless the woman is low risk (this means the woman must be younger than 25 years and have a body mass index less than 27, with no personal, ethnic or family risk factors) The Canadian Diabetes Association and the American College of Obstetricians and Gynecologists recommend universal screening. The U.S. Preventive Services Task Force found there is insufficient evidence to recommend for or against routine screening, and a 2017 a Cochrane review found that there is not evidence to determine which screening method is best for women and their babies.Some pregnant women and careproviders choose to forgo routine screening due to the absence of risk factors, however this is not advised due to the large proportion of women who develop gestational diabetes despite having no risk factors present and the dangers to the mother and baby if gestational diabetes remains untreated.