What is the recommended rate of consumption for the oral glucose tolerance test (OGTT) during gestational diabetes mellitus (GDM) screening?

From the Guidelines

You should drink the entire 50g or 75g glucose solution within 5 minutes for the glucose tolerance test during gestational diabetes screening. The standard recommendation is to consume it quickly but not so fast that it causes nausea or vomiting. Most healthcare providers instruct patients to finish the drink within 5 minutes, though some protocols allow up to 10 minutes. Drinking it too slowly can affect the accuracy of the test results, as the test is designed to measure how your body responds to a sudden glucose load. Drinking it too quickly may cause gastrointestinal discomfort. The timing of the test begins once you've finished the entire drink, and blood samples will be taken at specific intervals afterward (typically at 1 hour for the screening test or at 1,2, and 3 hours for the diagnostic test) 1. If you're concerned about the taste or potential nausea, you can request a chilled solution and drink it through a straw, which some women find makes it more tolerable.

Some key points to consider when taking the glucose tolerance test include:

• The test should be performed in the morning after an overnight fast of at least 8 hours 1.
• The diagnosis of gestational diabetes is made when any of the following plasma glucose values are met or exceeded: fasting 92 mg/dL, 1 hour 180 mg/dL, and 2 hours 153 mg/dL for the one-step strategy 1.
• The two-step strategy involves a 50-g glucose load test, and if the plasma glucose level is ≥130,135, or 140 mg/dL, a 100-g oral glucose tolerance test is performed 1.
• The American College of Obstetricians and Gynecologists notes that one elevated value can be used for diagnosis 1.

It's essential to follow the instructions provided by your healthcare provider and to ask any questions you may have before taking the test.

From the Research

Glucose Tolerance Test Drinking Speed

• The ideal drinking speed for the glucose tolerance test during gestational diabetes testing is not explicitly stated in the provided studies.
• However, a study from 1994 2 compared the effects of a standard 50-gm oral glucose solution and a modified, more physiologic 50-gm oral glucose solution on glucose values, insulin values, and side effects in pregnant women.
• The results showed that the modified solution, which was more dilute and palatable, resulted in more rapid absorption of glucose and decreased nausea and vomiting.
• Another study from 1990 3 found that a modified glucose solution with lower osmolarity resulted in more rapid gastric emptying and less nausea compared to the standard glucose solution.
• A study from 2025 4 compared the effects of two different drinking solutions on 2-h glucose values and gastrointestinal side effects, but did not specifically address the drinking speed.
• There is no direct evidence on the optimal drinking speed for the glucose tolerance test during gestational diabetes testing, but the studies suggest that a more physiologic and palatable solution may be better tolerated and result in more accurate results.

Factors Affecting Glucose Absorption

• The rate of glucose absorption can be affected by various factors, including the concentration and volume of the glucose solution, as well as individual factors such as gastric emptying and insulin sensitivity.
• A study from 2006 5 analyzed the disposition of a 2.5% glucose solution in patients with Type II diabetes and created a nomogram to guide fluid therapy.
• The study found that the disposition of glucose was an important factor governing fluid distribution, and that the volume of distribution of exogenous glucose was significantly larger than the volume of distribution of the fluid volume.
• Another study from 2019 6 compared the effects of different routes of glucose administration, including sublingual, buccal, and oral routes, on blood glucose concentrations and symptoms of hypoglycemia.
• The results showed that the sublingual route resulted in a higher blood glucose concentration after 20 minutes compared to the oral route in children with hypoglycemia and symptoms of concomitant malaria or respiratory tract infection.