This thesis focuses on the use of a child welfare principle in human assisted reproduction in the UK, as contained in section 13 (5) of the Human Fertilisation and Embryology Act 1990 (as amended). Given the principle is applied prior to conception, I argue that it should be distinguished from the familiarly known child welfare principle in child law and thus my focus is on the pre-conception welfare principle (PCWP). The aim of this thesis is to provide an argument for abolition of the PCWP from UK regulation. This thesis aims to add to the debate and complement the existing body of legal and philosophical literature which has critically analysed the function of the PCWP from various perspectives. It does so by highlighting the importance of terminology throughout the work and focusing on the broader implications of the PCWP in practice. I argue that the implications of the PCWP go far beyond its position in the legislation and in order to substantiate that central argument, I separate the function of the PCWP assessment into distinct categories of harm based regulation. Before doing so, however, I critically analyse the development of the PCWP; I consider its function as a regulatory method and I challenge whether it has a defendable ethical position in the current framework. Overall, I argue against the PCWP and the harm threshold rationale underpinning it in practice. In Part I, I first set out the background to this type of research and explain why this work is important for challenging unjustified state intervention on reproductive choice. Second, I set the scene by outlining the development of the welfare principle in child law; the legislative chronology of the PCWP and the function of Principles Based Regulation (PBR) in the current regulatory framework. This entails setting out a number of assumptions, arguments and debates surrounding the concepts of welfare and harm and how these have been framed in regulation; in addition to setting out a central theme of this thesis, which is an argument that the regulation of the PCWP does not meet requisite standards of consistent, transparent, objective, proportionate and contextually-sensitive regulation. These assumptions and vii arguments are vital for understanding the basis on which this work challenges the suitability of the PCWP in the current regulatory framework. Part II of the thesis contains the papers and delivers the arguments against the PCWP in sequence. The overall aim of Part II is to present the central argument of the thesis and answer the research questions set out in the introduction. To accomplish this, the thesis first explores how the borders of child welfare have been defined by child law and judge-made law in wrongful life cases or cases involving the withdrawal or withholding of treatment from sick children. This is followed by a chronological and comparative legislative assessment of the development of the regulation of child welfare in the context of the PCWP. This develops into the main argument of the thesis which demonstrates the application of PCWP in practice departs from benchmark standards of better regulation. The thesis moves on to provoke a fresh debate on the relationship between pre-conception child welfare and the familial and genetic harm thresholds which are mandated by the PCWP assessment. The concept of harm is explored in a philosophical sense and the arguments culminate in a contention that no single philosophy underpins the PCWP, and that there is therefore no good reason to retain a principle which is problematic in both a functional and substantive sense. The thesis concludes with an overview of the progression of the main themes in this thesis, as well as identifying some promising opportunities for future research which have arisen as a result of this work.