Objective: Accurate visual estimation of blood loss is critical for early recognition of obstetric haemorrhage. Despite its widespread use, visual estimation is prone to substantial bias. While professional experience has been shown to influence estimation accuracy, the potential contribution of gender-associated visual perceptual differences remains insufficiently explored . Design: We carried out a prospective observational simulation-based study at a tertiary university medical centre in Graz, Austria Setting/Sample: 50 physicians (28 females/22 males) were recruited from anaesthesiology and obstetrics. Eligibility required at least three months of clinical experience in obstetrics or obstetric anaesthesia. Clinicians with known colour-vision deficiency were excluded. Methods: All participants visually estimated blood loss in four simulated obstetric scenarios. The blood volumes and haemoglobin concentrations were verified by volume measurement and point of care testing. Each scenario was viewed individually under standardized conditions without access to physiological or contextual clinical information. Main Outcome Measures The primary outcome was absolute estimation error (mL) according to gender or professional background of participants. Secondary outcomes included scenario-specific accuracy and the association between self-rated confidence and estimation accuracy. Results: Women outperformed men in low and moderate volume scenarios. Across all scenarios the overall difference median absolute estimation error did not reach statistical significance. Professional background showed a stronger effect than gender: gynaecologists were significantly more accurate than anaesthetists across most scenarios (p < 0.001). Conclusions: Visual blood loss estimation accuracy in obstetric simulations is influenced by both gender and professional background. Gender-related differences appear volume-dependent, whereas professional experience exerts a consistent influence.