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Clin Chem. 2005 May;51(5):825-9. Epub 2005 Mar 11.

D-dimer concentrations in normal pregnancy: new diagnostic thresholds are needed.

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Emergency Medicine Research, Department of Emergency Medicine, Carolinas Medical Center, Charlotte, NC 28323-2861, USA.



Pregnancy is known to increase the D-dimer concentration above the conventional normal threshold of 0.50 mg/L, leading to an increased false-positive D-dimer test when venous thromboembolism (VTE) is clinically suspected in a pregnant patient. Our aim was to determine the effect of normal pregnancy on the D-dimer concentration.


Healthy women who were seeking to become pregnant and had no preexisting condition known to increase the D-dimer concentration were identified. Quantitative D-dimer measurements (MDA turbidimetric assay) and fibrinogen assays were performed before conception, at each trimester, and at 4 weeks postpartum. Patients were excluded for fetal loss or preeclampsia.


A total of 50 women were enrolled in the study, and blood samples were obtained at preconception and all trimesters from 23 women. The mean (SD) preconception D-dimer concentration was 0.43 (0.49) mg/L, and 79% of women had a D-dimer concentration <0.50 mg/L. D-Dimer increased with each trimester such that only 22% of women in the second trimester and none (of 23) in the third trimester (95% confidence interval, 0-14%) had a D-dimer concentration <0.50 mg/L. We found no correlation between either the D-dimer and fibrinogen concentrations or between the increases in D-dimer and fibrinogen with pregnancy.


Normal pregnancy causes a progressive increase in circulating D-dimer. The D-dimer test has no use in ruling out VTE in the third trimester if a cutoff of 0.50 mg/L is used. A large management study is needed to establish new thresholds for the D-dimer to rule out VTE in each trimester.

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