A term applied in medicine to a substance used as a substitute for another. The term is also applied to a woman who agrees to become pregnant and give birth to a child on the understanding that she will give up the child to the parents who have contracted with her for the surrogacy arrangement. When in vitro fertilisation (IVF – see under ASSISTED CONCEPTION) proved successful, it became possible to transfer a fertilised egg to a ‘uterus of choice’. Artificial insemination of the potential surrogate mother using sperm from the putative ‘father’ is also practised. Surrogacy has thrown up a host of ethical and legal problems.