If prenatal tests detect a genetic condition or abnormality in the fetus, a pregnant woman may be offered a termination under the serious handicap ground of the Abortion Act 1967, which applies in England, Scotland, and Wales. A termination is legal under this ground provided that "there is a substantial risk that if the child were born it would suffer from such physical or mental abnormalities as to be seriously handicapped". "Serious handicap" is not defined, and it is healthcare professionals' role to interpret its meaning. Two registered medical practitioners must be of the opinion, "formed in good faith", that the legal criteria have been fulfilled. This thesis aims to further understanding of how healthcare professionals decide whether a fetal condition is sufficiently serious for termination. Two phases of research addressed this aim: 1st phase: A systematic review that identified factors influencing healthcare professionals' viewpoints on whether a fetal condition is sufficiently serious for termination. Two syntheses were conducted; a narrative synthesis of 34 surveys, and a thematic synthesis of 14 qualitative studies. A range of medical and non-medical factors were identified. 2nd phase: Primary empirical research, comprising a context-specific Q-methodological study, which identified and systematically characterised the different ways the serious handicap ground is interpreted by healthcare professionals working in prenatal testing and terminations for fetal abnormality in the UK. Forty-eight participants completed a 36-statement Q-sort. Q-factor analysis produced four statistically independent viewpoints reflecting different interpretations. Findings are synthesised to provide a comprehensive description of how the viewpoints of healthcare professionals on whether a condition is sufficiently serious for termination are constructed. The ambiguities of interpreting the serious handicap ground are discussed. In addition, the implications of variation in interpretation of "seriousness" are considered in light of development of guidelines for healthcare professionals and the Abortion Act, should this ground be amended.