The glucose tolerance test in pregnancy: what to expect

The glucose challenge test (GCT) is a routine screening for gestational diabetes done between weeks 24–28. You'll drink a sweetened glucose drink (usually 50g of glucose) and have a blood draw one hour later to measure how your body processes sugar. No fasting is required beforehand.

If your result is above the threshold (typically 130–140 mg/dL depending on your provider's cutoff), you'll be asked to do the longer 3-hour glucose tolerance test, which does require fasting and involves four blood draws. About 15–25% of women fail the 1-hour screen, but only about a third of those are ultimately diagnosed with gestational diabetes. A positive screen is not a diagnosis — it's simply a flag for further testing.