It is widely accepted practice to describe couples who are unable to have a family as being ‘infertile’ but this is not always correct. Infertility is an inability to produce gametes and this accounts for only about half the cases in which couples are unable to have children. In the remainder, the individuals produce gametes normally but, for one reason or another, fertilisation and implantation of an embryo in the woman's womb is prevented or is contraindicated. It is, therefore, more correct to speak in terms of ‘childlessness’ to describe such a condition. The distinction is more than a matter of semantics and has practical consequences. It has been noted in Chapter 2 that assisted reproduction has a very low priority in the majority of National Health Service resource allocation programmes. One line of justification for this is to argue that, while the underlying cause – for example, disease of the Fallopian tubes – is certainly a matter of medical concern, the result, childlessness, is a social rather than a medical matter. Thus, although unblocking the tube would come within the ambit of the health authority, the provision of in vitro fertilisation (IVF) would not. This perspective may be arguable on both economic and ethical grounds, but it is mentioned in order to show that health authorities which do not provide IVF may have a tenable point of view.