Why low-dose aspirin persists in recurrent pregnancy loss without APS: cognitive bias and system design.

Low-dose aspirin (LDA) is widely prescribed for recurrent pregnancy loss (RPL) even when antiphospholipid syndrome (APS) is absent, despite high-level evidence showing no improvement in live-birth rate in such cases. In Japan and elsewhere, this empirical use persists across fertility and obstetric settings, suggesting a behavioral and systemic rather than purely evidentiary problem. This commentary interprets the persistence of LDA through the lens of cognitive bias and institutional design. At the cognitive level, action bias-the instinct to intervene when outcomes are uncertain-provides a sense of control for both patient and clinician after miscarriage. The availability heuristic further normalizes use because LDA is already familiar as prophylaxis for pre-eclampsia, and professional conformity (social proof) reinforces its legitimacy. Once started, status-quo bias and loss aversion make discontinuation difficult, as both clinician and patient fear regret if another loss occurs. Systemic structures amplify these biases. In Japan, time-intensive counseling is rarely reimbursed, whereas prescriptions are; ambiguous phrasing in domestic reports ("may consider aspirin") subtly encourages action over restraint. Discontinuity between fertility and obstetric care promotes pharmacologic reassurance in place of relational continuity. Together, these conditions transform an evidence-neutral intervention into a psychologically and institutionally self-reinforcing default. Recognizing this pattern reframes empirical LDA as a system phenomenon rather than individual error. Practical countermeasures include bias-awareness education, explicit "do-not-start" criteria limiting LDA to APS-confirmed cases, audit and feedback cycles, and shared decision aids that display live-birth data from randomized trials. Above all, continuity-based reassurance-scheduled follow-up and early-pregnancy access without unnecessary medication-can restore alignment between evidence and empathy. Understanding the cognitive architecture of empirical LDA use enables reproductive medicine to redesign its environment so that good science and good care no longer compete. Recognizing these dynamics can help clinicians and institutions redesign care environments that support evidence-based restraint without diminishing empathy.