Background: Intra-cranial haemorrhage (ICH) in neonates with haemophilia A (HA) remains a serious perinatal complication. Prophylactic administration of emicizumab (Emi) to pregnant HA carriers has been discussed as a potential preventive strategy, although current clinical evidence is limited to one case report. This study evaluated whether ex vivo addition of Emi further augments coagulation potential in late pregnancy.
Methods: Plasma samples were obtained from 62 healthy pregnant women and five pregnant HA carriers during late gestation. Emi (50 µg/mL) was added ex vivo, and coagulation potential was assessed using the thrombin generation assay (TGA) and clot waveform analysis (CWA). TGA parameters included time to thrombin peak (ttPeak), peak thrombin (PeakTh) and endogenous thrombin potential (ETP). CWA parameters included clot time (CT) and adjusted coagulation velocity (Ad|min1|).
Results: FVIII activity was elevated in both groups. Emi induced modest shortening of ttPeak in healthy women (9.3-8.5 min) and in carriers (9.3-8.3 min). PeakTh was unchanged in healthy women before and after Emi addition and showed a small reduction in carriers. ETP did not change in healthy women, whereas a slight decrease was observed in carriers. CWA demonstrated a small but statistically significant shortening in CT and increases in Ad|min1| in both groups. Overall, Emi-induced changes of coagulation potential across assays were modest and generally within assay variability.
Conclusion: These findings ex vivo indicated that Emi at clinically relevant concentrations does not meaningfully enhance the hypercoagulable state characteristic of late pregnancy. In vivo studies are required to confirm the safety of maternal prophylaxis.
Keywords: bispecific antibody; carrier; coagulation; haemophilia A; pregnant.
© 2026 John Wiley & Sons Ltd.