How to Fast for a Glucose Tolerance Test

A glucose tolerance test checks how your body handles a measured glucose drink. The service may take a fasting blood sample, ask you to drink the solution, and collect further samples after a set interval. Food, sweet drinks, chewing gum, smoking, strenuous activity, and some medicines can affect the test process, so instructions may be specific to your clinic.

Fasting rules can differ according to the test requested and your pregnancy care plan. Do not assume that tea, coffee, juice, or milk is allowed. If you have diabetes, feel faint when fasting, or take regular medicine, ask for an individual plan before the appointment.

Confirm the appointment time, when fasting should start, whether plain water is allowed, and which medicines to take. Eat normally in the days before the test unless your clinician gives different advice; changing your usual diet to influence the result is not helpful. Bring a snack for after the final sample, wear comfortable clothing, and plan to remain at the clinic during the testing period.

If you accidentally eat or drink something outside the instructions, tell the staff before the first sample. They can decide whether to continue, reschedule, or record the circumstances. Learn more about the [Glucose Tolerance Test](/treatments/pregnancy-and-birth-care/glucose-tolerance-test/) and how it fits into an [Antenatal Care Package](/treatments/pregnancy-and-birth-care/antenatal-care-package/).

Tell the clinic before fasting if you have a condition or medicine that makes missed meals unsafe. During preparation or testing, ask for help if you develop severe dizziness, fainting, confusion, repeated vomiting, or feel acutely unwell. Do not drive if you feel unsafe after the test.

Ask exactly when fasting begins, which drinks are permitted, whether medicines should be taken, what happens if you vomit the glucose drink, and when you will receive the result.