Abstract Study question What are the practical and ethical complexities emerging from the increasing offer of ECS in the UK amidst a lack of guidance and regulation? Summary answer The current lack of guidance and regulation around ECS in the UK raises complex practical and ethical issues both for technology users and providers. What is known already Expanded carrier screening (ECS) is increasingly offered preconception to identify risks of passing on genetic conditions to offspring. It involves testing of people with no known risk for hundreds of conditions and can be used for prospective parents or gamete donors. Despite increasing uptake in the UK, ECS has received little policy attention compared to PGT and newborn screening, leaving clinics and laboratories free to determine its cost, delivery and marketing. While the ethical and medical implications of ECS have been considered, issues for practitioners and policymakers are under-researched, with little understanding of specificities in the UK context. Study design, size, duration Using a scoping methodology (Arksey H & O’Malley L., 2005), this study aimed to situate ECS in the UK policy landscape. 20 qualitative interviews were conducted with stakeholders (policy, commercial, patient, professional) over 6 months (July - December 2023) to systematically capture emergent policy and practice issues. Participants/materials, setting, methods Data come from part 1 of a large ESRC-funded interdisciplinary, multi-method project investigating the social, ethical, economic and policy implications of ECS in the UK. Semi-structured interviews (Van Audenhove, L., & Donders, K. 2019) were conducted with 20 key policy, commercial, and clinical stakeholders with a remit or interest in regulating reproductive genomic testing in the UK. Participants were recruited using purposive sampling, informed by a literature review and consultation with experts in the field. Main results and the role of chance Despite the UK government’s aspiration to become a world-leader in genomic medicine, there has been little public and policy discussion around ECS. ECS does not appear on the agenda of several key UK policy organisations, and some policy stakeholders interviewed were unaware of the specific complexities presented by ECS. Guidance is currently under discussion among some professional societies. The current lack of guidance has generated a range of practical and ethical issues for providers and users including: • Inconsistent provision of genetic counselling about the technology aims, results and limitations; • Shortage of genetic counsellors; • Difficulties and confusion about how to use imported ECS-screened donated gametes; • Lack of clarity regarding legal liability if a recessive condition is transmitted via gamete donation, leading to defensive practise; • Unequal access to ECS offer and services; • Lack of communication and collaboration between the public and private sectors around ECS; leading to extra costs and difficulties for users and challenges for the NHS Clinical Genetics services; • Difficulties related to the absence of a standard panel of conditions; Absence of clear and evidence-based information for test-takers in the public domain. Limitations, reasons for caution We used a purposive sample. Given there is limited information about where and how ECS is currently offered and that some providers do not advertise their offer, we may not have represented the views of all provider and marketing stakeholders. Wider implications of the findings This research shows the need for the development of appropriate policy, guidance and regulation and public discussion in the UK. In particular, there is a need for better communication and collaboration around ECS between the public and private sectors. Trial registration number Non applicable