Introduction.D-dimer levels increase throughout pregnancy, hampering the usefulness of the conventional threshold for dismissing\nthromboembolism. This study investigates the biological fluctuation of D-dimer in normal pregnancy. Methods. A total of 801\nhealthy women with expected normal pregnancies were recruited. D-dimer was repeatedly measured during pregnancy, at active\nlabor, and on the first and second postpartum days. Percentiles for each gestational week were calculated. Each individual D-dimer\nwas normalized by transformation into percentiles for the relevant gestational age or delivery group. Therange in percentage points\nduring the pregnancy and the delivery was calculated, and reference intervals were calculated for each pregnancy trimester, during\nvaginal delivery and scheduled and emergency cesarean section, and for the first and second day postpartum. Results. D-dimer\nincreased during pregnancy; the maximal fluctuation was approximately 20 percentile points in approximately half of the women.\nIn one out of ten women, the D-dimer values fluctuated by more than 50 percentile points. Conclusions. Due to the biological\nvariation in D-dimer within each individual woman during normal pregnancy, repeated D-dimer measurements are of no clinical\nuse in the evaluation of thromboembolic events during pregnancy.
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