GDM can be diagnosed at any point during a pregnancy. However, the typical time frame of diagnosis is between 24 and 28 weeks of gestation. Although a variety of screening methods have been used, the glucose challenge test (GCT) and the fasting plasma glucose (FPG) test are believed to be the best predictors of GDM. The World Health Organization (WHO) also recommends utilizing the oral glucose tolerance test (OGTT); a test that measures the ability of the body to use glucose (the body’s main source of energy).
Diabetes Canada recommends a preferred and an alternative approach for the screening and diagnosis of GDM. The preferred approach involves using 50 g GCT and/or 75 g OGTT, while the alternative approach uses only the 75 g OGTT (Diabetes Canada Clinical Practice Guidelines Expert Committee, 2018). Both the GCT and OGTT involve drinking a sweet liquid containing a measured amount of glucose, after which blood samples are collected at timed intervals usually one or two hours after drinking the liquid. For more information on the screening and diagnosis of GDM, please visit: Screening and Diagnosis for Gestational Diabetes.