Understanding the glucose tolerance test

During pregnancy, hormonal changes can make it harder for insulin to keep blood glucose in its usual range. The test helps identify gestational diabetes, which can have no obvious symptoms. It is different from checking urine or using a home glucose meter because the clinic compares your response over a defined period.

The appointment commonly begins with a fasting blood sample. You then drink a glucose solution and remain at the clinic while further blood samples are taken. Follow the clinic's instructions about fasting, medicines and arrival time; eating or drinking when asked not to can affect the interpretation.

Ask whether you should fast, and tell the team about medicines, illness or vomiting before the appointment. Bring water for after the test and something to eat once staff say it is allowed. The drink may taste very sweet, and some people feel nauseated, light-headed or tired while waiting. Sit quietly and tell staff promptly if you feel unwell or vomit.

If the result suggests gestational diabetes, your maternity team may arrange nutritional advice, glucose monitoring or further review. A result is interpreted with your pregnancy details and the clinic's threshold, not in isolation.

The test itself is not usually an emergency, but contact your maternity team if you cannot keep the drink down, become faint, or feel seriously unwell. Seek urgent help for confusion, collapse, severe weakness or breathing difficulty. After an abnormal result, attend the recommended follow-up so a management plan can be made.

Ask why the test is recommended, how long fasting lasts, which medicines you should take, when results will be available, and what follow-up would happen if the result is outside the expected range.