D-dimer during pregnancy: establishing trimester-specific reference intervals.

Pregnancy is associated with an increased risk of venous thromboembolism (VTE). D-dimer is a biomarker used as an exclusion criterion of VTE disease, but its usefulness during pregnancy shows limitations because D-dimer levels physiologically increase through pregnancy. The aim of our study was to follow the changes of D-dimer levels and to establish trimester-specific reference intervals during normal pregnancy. This is a longitudinal prospective study in which the reference population finally included 102 healthy pregnant women. Plasma D-dimer levels were measured during the three trimesters of pregnancy, using a latex-based immunoturbidimetric assay. Reference intervals were calculated according to the Clinical and Laboratory Standards Institute recommendations. D-dimer levels increased progressively and significantly through pregnancy and peaked in the third trimester, in which D-dimer levels were above the conventional cut-off point (500 µg/L) in 99% of pregnant women. The following reference intervals were defined: first trimester: 169-1202 µg/L, second trimester: 393-3258 µg/L and third trimester: 551-3333 µg/L. The study provides reference intervals of D-dimer during the pregnancy using latex-based immunoturbidimetry on the ACL 300 TOP automated coagulation analyser. Further prospective studies of pregnant women with clinical suspicion of VTE are needed to validate these results.