Haemostatic Alterations During Pregnancy Across Trimesters in Healthy Women at a Tertiary Hospital in Imo State, South East Nigeria

Pregnancy induces a progressive physiological hypercoagulable state intended to minimise haemorrhage at delivery, but these changes may predispose susceptible women to thromboembolism, necessitating trimester-specific reference intervals for accurate clinical interpretation. This study characterised haemostatic alterations across all three trimesters in healthy pregnant women at Federal Medical Centre Owerri, Imo State, South East Nigeria. A prospective longitudinal study followed 90 healthy singleton pregnant women with samples collected at 8-12 weeks, 20-24 weeks, and 34-38 weeks gestation, and again at 6 weeks postpartum as a reference baseline. Prothrombin time, activated partial thromboplastin time, fibrinogen, D-dimer, protein C, protein S, antithrombin III, von Willebrand factor antigen, and platelet count and function were measured at each timepoint. Fibrinogen increased progressively across trimesters, reaching a peak of 5.8 g/L in the third trimester. D-dimer rose significantly in the second and third trimesters, rendering conventional non-pregnant cut-offs invalid. Protein S declined significantly in the second trimester. Antithrombin III remained stable. vWF antigen increased progressively. Platelet counts showed a mild reduction in the third trimester without clinical thrombocytopaenia. Postpartum values returned towards baseline by six weeks. The study establishes Nigerian-specific trimester-referenced haemostatic intervals and demonstrates the invalidity of non-pregnant coagulation reference ranges in antenatal assessment, recommending adoption of trimester-specific laboratory reference intervals in obstetric units across South East Nigeria. Keywords: haemostasis, pregnancy, hypercoagulability, fibrinogen, D-dimer