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


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
Kline
Jeffrey A
JA
Emergency Medicine Research, Department of Emergency Medicine, Carolinas Medical Center, Charlotte, NC 28323-2861, USA. Jkline@carolina.rr.com
Williams
Ginger W
GW
Hernandez-Nino
Jackeline
J
D000328:Adult; D005260:Female; D005338:Fibrin Fibrinogen Degradation Products / Q000032:analysis*; D005340:Fibrinogen / Q000032:analysis; D006801:Humans; D011247:Pregnancy / Q000097:blood*; D011264:Pregnancy Trimesters; D012016:Reference Values
D005338:Fibrin Fibrinogen Degradation Products; C036309:fibrin fragment D; D005340:Fibrinogen