BACKGROUND: The oral glucose tolerance test is a common method of diagnosing gestational diabetes mellitus. This test causes several unpleasant side effects such as nausea, vomiting, abdominal bloating, and headache. OBJECTIVE: This study aimed to assess the effect of liquid temperature and additives on pregnant women's taste perception, side effects, and glycemic levels in an oral glucose tolerance test. STUDY DESIGN: This study was a single-center, randomized, and multi- and open-arm clinical trial. A total of 399 participants receiving the 75-g oral glucose tolerance test for gestational diabetes mellitus diagnosis were included. Solutions for use in the 75-g oral glucose tolerance test were prepared in 8 formulas, with the participants randomly assigned to 1 of the 8 groups: room-temperature water, hot water, cold water, hot water with tea bag, room-temperature water with tea bag, cold water with tea bag, room-temperature soda water, and cold soda water. The main study outcomes were glycemic levels, satisfaction, perceived taste, side effects, and gestational diabetes mellitus. Glycemic levels were measured when fasted and at 1 hour and 2 hours after glucose administration. Satisfaction, taste perception, and side effects were evaluated immediately after the oral glucose tolerance test, and gestational diabetes mellitus was determined on the basis of glycemic levels. RESULTS: The cold soda water solution led to a significantly higher glycemic level at 1 hour after glucose intake compared with room-temperature soda water solution (P=.009). Glucose formula was found to not significantly affect gestational diabetes mellitus incidence (P>.05) or the participants' satisfaction, vomiting, headache, or abdominal bloating (P>.05). However, the formula did significantly affect perceived taste (P=.027) and the degree of nausea (P=.014). CONCLUSION: Several glucose solutions, such as cold glucose solution and any-temperature glucose solution containing a tea bag, led to slightly higher taste scores and a lower degree of nausea compared with the room-temperature water-based glucose solution. However, soda water was found to affect the glycemic level at 1 hour after glucose intake, and is not suggested for use for gestational diabetes mellitus diagnosis.