Summary
Haemostatic reference intervals are generally based on samples from non-pregnant women.
Thus, they may not be relevant to pregnant women, a problem that may hinder accurate
diagnosis and treatment of haemostatic disorders during pregnancy. In this study,
we establish gestational age-specific reference intervals for coagulation tests during
normal pregnancy. Eight hundred one women with expected normal pregnancies were included
in the study. Of these women, 391 had no complications during pregnancy, vaginal delivery,
or postpartum period. Plasma samples were obtained at gestational weeks 13–20, 21–28,
29–34, 35–42, at active labor, and on postpartum days 1 and 2. Reference intervals
for each gestational period using only the uncomplicated pregnancies were calculated
in all 391 women for activated partial thromboplastin time (aPTT), fibrinogen, fibrin
D-dimer, antithrombin, free protein S, and protein C and in a subgroup of 186 women
in addition for prothrombin time (PT), Owren and Quick PT, protein S activity, and
total protein S and coagulation factors II, V, VII, VIII, IX, X, XI, and XII. The
level of coagulation factors II, V, X, XI, XII and antithrombin, protein C, aPTT,
PT remained largely unchanged during pregnancy, delivery, and postpartum and were
within non-pregnant reference intervals. However, levels of fibrinogen, D-dimer, and
coagulation factors VII, VIII, and IX increased markedly. Protein S activity decreased
substantially, while free protein S decreased slightly and total protein S was stable.
Gestational age-specific reference values are essential for the accurate interpretation
of a subset of haemostatic tests during pregnancy, delivery, and puerperium.
Keywords
Fibrin D-dimer - haemostasis - normal pregnancy - protein C - protein S - reference
interval
