OBJECTIVE: The aim of the research is to examine whether certain metabolic and immunological indicators from the blood of pregnant women measured during the 1st and 3rd trimesters of pregnancy can serve as predictive and/or diagnostic biomarkers in the early detection of gestational diabetes. STUDY DESIGN: The research was organised as a prospective cohort study. PARTICIPANTS AND METHODS: 30 pregnant women who were currently in good general condition and without known immune diseases were included in the research. During the 1st and 3rd trimesters of pregnancy, pregnant women filled out questionnaires with questions about pregnancy. After filling out each questionnaire, peripheral venous blood was taken from the pregnant women. Pregnant women are classified into different categories depending on their risk for developing gestational diabetes. Various biochemical indicators related to gestational diabetes were analyzed from venous blood samples. RESULTS: During the 1st trimester, high-risk pregnant women have higher hemoglobin values and lower CRPa values compared to low-risk pregnant women, and in the 3rd trimester, they have lower B-lymphocyte values (CD19+CD5+) compared to low-risk pregnant women. Diabetic women during the 1st trimester have lower values of lymphocytes, insulin and HOMA-IR compared to the high-risk group, while in the 3rd trimester there is no significant difference between the two groups. In a comparison of low-risk pregnant women and diabetic women, the latter have a significantly lower value of B-lymphocytes (CD19+CD5+) during the first and third trimesters. There is no significant association between hemoglobin and HbA1c during the 1st and 3rd trimesters. CONCLUSION: There is a difference between certain biochemical indicators according to trimesters depending on the category of pregnant women according to the risk for developing gestational diabetes. Most of the analyzed indicators showed low sensitivity or specificity to be able to serve as a biomarker of gestational diabetes, except for B-lymphocytes (CD19+CD5+) which could be a biomarker.