In plain words
A glucose tolerance test measures how well the body clears sugar from the blood. The person drinks a sweet glucose drink after fasting. Blood is drawn before the drink and again at set times, often one and two hours later. Sometimes a longer test is used. In pregnancy, it is the usual way to check for . Some clinicians use a one-hour screen first, and then the full test if the number is high. Many people find the drink very sweet and feel queasy. Results are read against published cut-offs. A result above a cut-off is a reason for further evaluation, not a diagnosis by itself.
The deeper version
The measures plasma glucose before and at intervals after a standardized glucose load, typically 75 grams in a one-step approach or 100 grams over three hours in the two-step Carpenter and Coustan approach (O'Sullivan and Mahan, Diabetes, 1964; Carpenter and Coustan, American Journal of Obstetrics and Gynecology, 1982). The 50-gram one-hour screen is a first-step test that flags more people for the full test. ACOG Practice Bulletin 190 (2018) lays out screening and diagnostic pathways. Test performance depends on fasting status, glucose load, sample handling, and timing. Nausea, early-morning sickness, and recent food intake can affect results. The controversy concerns the choice of load and cut-offs, whether a one-step or two-step approach improves outcomes, and how much variation in diagnosis reflects test conditions rather than disease.
Where it comes up
- Gestational diabetesPregnancy: Your Body
- Eating with gestational diabetesPregnancy: Eating
- The six-week checkup (and why it isn't enough)Postpartum: Your Body
- Pregnancy at 35 and olderPregnancy: Your Body
What mothers here say about glucose tolerance test
No one has posted under this term yet.
Sources
- O'Sullivan JB and Mahan CM — Criteria for the oral glucose tolerance test in pregnancy. Diabetes, 1964
- American College of Obstetricians and Gynecologists — Practice Bulletin 190: Gestational diabetes mellitus (2018)