Abdul Mannan: Pregnancy Changes Almost Every Coagulation Test
Abdul Mannan, Director Haemophilia Centre at Betsi Cadwaladr University Health Board, shared a post on LinkedIn:
“Pregnancy Changes Almost Every Coagulation Test
Pregnancy is nature’s largest coagulation experiment.
As gestation progresses:
↑ Factor VIII
↑ Von Willebrand factor
↑ Fibrinogen
↑ D-dimer
↓ Protein S activity
↓ Antithrombin
↓ Factor XIII
The result is a physiological hypercoagulable state.
Why it matters at the bench and the bedside:
D-dimer rises through pregnancy, so it becomes unreliable for excluding VTE
Protein S falls, so testing for protein S deficiency in pregnancy is not reliable
Thrombosis risk climbs
Mild bleeding disorders can look temporarily corrected
There is a practical consequence here. Most of these changes take 6 to 7 weeks postpartum to settle, and some variables can take up to 12 weeks. That is why haematologists usually wait at least 12 weeks postpartum before using lab tests to exclude conditions like von Willebrand disease.
Normal pregnancy is not normal haemostasis.
Samuelson Bannow B et al. Lancet Haematology 2026. DOI: 10.1016/S2352-3026(26)00110-9.”
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