Both the Canadian Diabetes Association and the American Diabetes Association recommend that all pregnant women be screened for gestational diabetes between 24 and 28 weeks gestation, and earlier if high risk factors are present. These factors are:
- previous GDM
- family history of diabetes
- previous large-for-dates baby
- South or East Asian, Hispanic, African, Native North American, or Pacific Islands ancestry
- multiple pregnancy
- previous birth defect
- previous stillbirth or spontaneous miscarriage
- history of gestational hypertension, urinary tract infection, polyhydramnios (ADA)
Testing may be done as a 1 step (75gram GTT) or a 2 step (50gram screen and 75gram GTT) process. The following values are used in BC for the 75gram GTT:
Fasting ≥ 5.1 mmol/L
1 hour ≥ 10.0 mmol/L
2 hour ≥ 8.5 mmol/L
For comprehensive information on diagnosis and treatment of GDM, please refer to the 2013 CDA Clinical Practice Guidelines for Diabetes and Pregnancy.
These women will need to follow a diet and exercise program, and may need insulin to control their blood glucose. Oral hypoglycemic agents are not currently recommended as a safe and effective choice in pregnancy in Canada. Well controlled gestational diabetes results in normal outcomes for the mother and the baby (Thompson et al, 1994).
Women who have a high 50 gm screen but are unable to tolerate the GTT or those with asymmetrical macrosomia on ultrasound are also at risk.