Navigating the unexpected: management of incidental severe Factor V deficiency in term pregnancy.

Severe Factor V deficiency (parahaemophilia) is a rare autosomal recessive coagulation disorder with a highly variable clinical phenotype. We report the incidental detection of isolated severe Factor V deficiency (<1% activity) in a completely asymptomatic primigravida during routine preoperative evaluation prior to an elective caesarean section. Despite marked prolongation of prothrombin time and activated partial thromboplastin time, the patient had no prior bleeding history. Mixing studies and a normal thrombin time localised the defect to the common pathway, which was confirmed by factor assay. Management involved multidisciplinary planning, peri-operative fresh frozen plasma transfusion and avoidance of neuraxial anaesthesia. The patient underwent caesarean section under general anaesthesia and delivered a healthy neonate without maternal or neonatal complications. This case highlights the poor correlation between plasma Factor V levels and bleeding phenotype and underscores the diagnostic value of thrombin time in evaluating common pathway coagulation defects.