Background/Objectives: Pregnancy is associated with increased procoagulant conditions, and when combined with obesity, it can elevate the risk of thrombosis. The study aims to assess thrombosis risk markers during pregnancy in relation to obesity. Methods: Somatically healthy women aged 18–42 years with spontaneous pregnancies who did not receive specific antithrombotic treatment were enrolled in the study (n = 97). The participants were divided into groups based on pregestational BMI: the first group consisted of patients who had a BMI ≤ 25 (n = 42), and the second group consisted of patients who were overweight (BMI > 25) and obese (BMI > 30) (n = 55). The control group comprised healthy, non-pregnant, non-obese women (n = 10). Results: Fibrinogen levels, elevated during pregnancy, were higher in the II and III trimesters, with gestational period having a greater influence than BMI. Moderate D-dimer accumulation was observed regardless of obesity, but higher levels were seen in obese women during the III trimester, indicating the dissolution of intravascular fibrin deposits. Soluble fibrin was significantly higher in obese and overweight women during the II trimester and elevated in both groups during the III trimester, correlating with D-dimer accumulation and indicating thrombus formation. A decrease in platelet aggregation ability was observed correlating with D-dimer and soluble fibrin patterns. Conclusions: A significant accumulation of thrombosis risk markers was observed in the III trimester compared to the II, occurring earlier in obese and overweight pregnant women and indicating a higher risk of thrombotic complications in obesity.

Thrombotic events are among the most dangerous complications of pregnancy. Therefore, selection of appropriate tests and standardization of techniques used for accurate diagnostics of blood coagulation system state is of great importance. In this present study, we monitored several molecular markers of the dangers of intravascular thrombus formation and estimated the platelet function in pregnant women during­ gestation. We performed independent measurements using the same methodology for different cohorts of patients recruited in Kyiv (Ukraine) and in Szeged (Hungary). D-dimer and soluble fibrin were measured using ELISA. Protein C (PC) level was estimated using chromogenic substrate assay. Fibrinogen concentration was measured by spectrophotometry using thrombin-like enzyme. Platelet function was estimated by aggregometry­. Statistical data analysis was performed using the Kruskal-Wallis test. Statistically significant increases of fibrinogen concentration from first to third gestational trimester was shown for both studied cohorts of patients (5-6 mg/ml at third trimester on average). Applied methods allowed us to detect the same tendencies of decreases in PC level as well as the appearance of moderate amounts of D-dimer (up to 300 ng/ml) and SF (up to 10-15 ug/ml). Platelet function was increased on the first trimester of pregnancy and decreased during­ following trimesters slightly. Results indicated the changes in the blood coagulation system of pregnant women during gestation with the same effectiveness independently of the selected cohorts, time and place of measurements. The application of the proposed diagnostics algorithm may allow estimating the risk of thrombotic complications during pregnancy. Keywords: D-dimer, fibrinogen, platelets, pregnancy, soluble fibrin, thrombosis