The occurrence of gestational diabetes has increased recently. This condition, which can have extremely negative consequences for both mother and baby, can be detected by using an oral glucose tolerance test, and remedial action can be taken to prevent or reduce complications based on the results of the test. However, information about the oral glucose tolerance test (the OGTT) from different sources can negatively affect pregnant women and their families, resulting in their not taking the test. The aim of this study is to determine the knowledge and attitudes of women in the third trimester of pregnancy in relation to the OGTT. This descriptive cross-sectional study was conducted at two university hospitals between October 2017 and June 2018. The voluntary participants comprised 303 pregnant women in the third trimester of pregnancy. The research data were collected using "Demographic Data Collection Form and Determination Form for the OGTT Screening Status of Pregnant Women." The relationship between categorical variables was analyzed using chi-square tests. The percentage of pregnant women who did not have the OGTT monitoring was 32.7%. The main reasons for this were media exposure (28.6%), lack of knowledge (19.4%), and doctor's recommendation (19.4%). Forty-three percent of the pregnant women who did not have the OGTT were not aware of why the test done and 73.3% thought that the OGTT was dangerous for the baby. Of these, 58.8% of pregnant women received the information about the OGTT from doctors and 41.2% from midwives and nurses. A significant difference was found between the OGTT status of women according to their place of residence, number of pregnancies, knowledge about why the OGTT is performed, information sources, and the belief that the test is dangerous to the health of mother and baby (p < 0.05). Not having OGTT screening during pregnancy can lead to irremediable negative complications for the health of both mother and baby.