This article describes an external pilot study of a modified 'partially randomised patient preference' trial comparing a web-based intervention (designed to promote mental wellbeing) with standard care post-miscarriage. Assessment comprised an online administration of baseline measures with follow-up at 3 months following registration. Baseline data were obtained from 60 women (and seven partners) post-discharge from one of two Early Pregnancy Assessment Units. 'Intention to treat' versus a 'per protocol' sensitivity analysis showed the effects of introducing a 'preference' option post-randomisation, and highlights the benefits compared with a randomised controlled trial design to enable a robust evaluation of the website in promoting mental wellbeing after miscarriage.