The technology which has enabled men and women who would naturally be infertile to have children has also produced some serious ethical issues. Each society needs to think about these issues and decide what should be done about them. Here are some of the issues.

A frozen harvest

Most IVF clinics now offer embryo freezing and storage to their clients. The early embryos are frozen and stored in flasks of liquid nitrogen. Human sperm have been frozen and stored for many years. The use of frozen human embryos is much more recent, although animal embryos have been transported around the world in this way for some time. It seems a very dramatic treatment for such delicate tissue, but when Zoe Leyland was born in Australia in 1984, the first frozen embryo to become a live baby, she seemed to have suffered no ill effects from her time in the deep freeze!

Freezing embryos has many advantages. If the first attempt at IVF fails the couple can have at least one, if not more, attempts without having to go through the whole process of fertility drugs and egg collection again. If, on the other hand, the first attempt is successful, then the remaining embryos can be kept so that, if and when the couple decide they would like another child, they have embryos ready to go. Again this makes the whole process quicker, less traumatic and less expensive for all concerned. However, the presence of these frozen embryos raises some questions. One of the simplest is - what happens to the embryos once a couple decide their family is complete?

The embryos may simply be destroyed, but this is not the most usual fate for them. If the parents are willing - and they often are - the embryos may be used for further research into the treatment of human fertility. They may be allowed to continue developing until they are 14 days old - all research on older embryos is banned in the UK and many other countries follow that same advice. Another alternative is that one couple may donate their 'spare' embryos to another infertile couple who cannot produce healthy embryos. Many other couples decide to keep their frozen embryos 'just in case' - although most clinics put a limit on the number of years they will keep the embryos before disposing of them.

Another ethical problem involves the situation if the parents of those embryos after divorce - to whom do the embryos belong? This is an important issue, because ultimately the parents of the embryos decide what is to become of them, and if the couple are divorced and do not agree about the fate of the embryos, who then takes responsibility for them? Another scenario which must be considered is if both parents die in an accident before they have successfully had children. If there are still healthy frozen embryos , should they be implanted inside a surrogate mother and brought into the world to inherit their parents belongings?

In all of these debates the welfare of the potential children has to be paramount. It could be extremely damaging for children to feel that they had been pawns in their parents divorce settlement or brought into being to make sure money stayed in the family.

In theory, frozen embryos could be kept for around 10 000 years before the natural background radiation of the earth damaged their DNA to the extent that they would not grow and develop properly. In the UK there are legal limits - frozen embryos can only be kept for five years, with another five years extension possible if the parents want more time to decide if they want to add to their family. This gives a total of ten years embryo storage. As no-one knows for certain how long frozen embryos can be stored safely this limit attempts to protect children who might be born damaged in some way from eggs which had been stored for longer than 10 years. Other countries have less strict laws and regulations about this. This again raises child welfare issues, making it possible for one sibling to be thirty or even forty years younger than the other. But whatever the legal situation, the existence of frozen embryos raises difficult issues.