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

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 (R). 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.