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Changes in fibrin D-dimer, fibrinogen, and protein S during pregnancy

Abstract Background. Pregnancy is a hypercoagulable state with a 5- to 10- fold higher risk of venous thromboembolism. Existing reference intervals for fibrin D-dimer (D-dimer), functional fibrinogen (fibrinogen) and protein S, free antigen (protein S) are based on non-pregnant patients and reference intervals for pregnant patients are warranted. Objectives. The aim of the present study was to contribute to the establishment of reference intervals for D-dimer, fibrinogen and protein S during pregnancy and to discuss the use of the analyses during pregnancy. Methods. We included 55 healthy pregnant women in gestational week 11–17, with normal current pregnancy. Blood samples were collected in gestational weeks 11–17, 21–27 and 34–37. The three plasma parameters D-dimer, fibrinogen and protein S were analysed by STA-R Evolution®. Results. A significant rise in D-dimer was found from first to second trimester (p < 0.0001) and from second to third trimester (p < 0.0001). The level of fibrinogen rose significantly from second to third trimester (p < 0.0001). Protein S showed a statistically significant fall in the level from first to second trimester (p < 0.0001) and remained stable thereafter. Conclusion. Changes during pregnancy in plasma D-dimer, protein S and fibrinogen were confirmed. Further clinical studies are needed to clarify a clinical useful cut-off point for D-dimer in pregnancy. We suggest careful attention to a low peripartum fibrinogen, since it indicates an increased bleeding risk. We confirmed an earlier suggested lower cut-off point for protein S, during pregnancy.