Pregnant people are screened for gestational diabetes at 24 to 28 weeks of gestation. Screening methods vary and may include a one- or two-step approach.[1][2] The two-step approach is more common in the US. Both approaches use an oral glucose tolerance test (OGTT), which involves drinking a sugar-containing beverage and then taking blood samples to see how high blood sugar rises in response to the drink. If blood sugar levels are higher than established normal ranges, gestational diabetes may be diagnosed.
Some pregnant people have a higher risk of gestational diabetes and may be screened before 24 weeks gestation to identify pregestational diabetes (diabetes that was present before pregnancy) and early gestational diabetes. The best test for early screening is unclear, but fasting blood glucose levels, HbA1c values, and/or OGTT are often used.[2][3]