In the 30 years since Louise Brown became the first test- tube baby, fertility treatment has come so far that it now accounts for one UK birth in 100. Yet there are still patients for whom it can do little. Men who make no sperm, and women with no eggs, must rely on adoption, donor conception or surrogacy if they want to start a family. That situation, however, may soon change because of advances in stem cell research.Sperm grown from embryonic stem cells have already been used to produce mouse pups, and scientists are trying to use similar techniques to make human reproductive cells, or gametes. This week, the Hinxton group - a panel of stem cell experts - predicted that success could be as little as five years away.

The next step would be to make “artificial gametes”. Cells from an infertile man or woman would first be reprogrammed into an embryonic state, or used to make cloned embryonic stem cells. The resulting stem cells would then be turned into sperm or eggs, which would carry the patient's DNA.Many of those this technology would benefit have survived childhood cancers, diagnosed when they were too young to freeze sperm or eggs to preserve fertility. Others are women who have suffered the distress of early menopause. This is medical science at its compassionate best.

Not everybody, however, has seen it quite like that. Whenever new developments in this field are reported, they invariably prompt speculation that the technique might be used to allow lesbians to produce sperm, and gay men eggs. Homosexual couples might thus have a child with genetic material from both partners, in a way that is unthinkable in nature. Worried discussions about what this might mean for sexual politics often drown out dialogue on the benefits for infertile patients.

The Daily Telegraph, for instance, reported the Hinxton group's findings on Tuesday under the headline: “Same-sex couples could produce children”. That was strange considering that the Hinxton scientists actually took pains to point out that this is not going to be on the agenda any time soon. Our sex is determined by the inheritance patterns of the X and Y chromosomes: women have two copies of the X, while men have one X and one Y. This is critical to the formation of gametes, and will make it very difficult to create them from cells of the opposite sex. As eggs are more complex than sperm, experts think it will be hard enough to make them from XX stem cells, let alone from male ones. And as working sperm require genes on the Y chromosome, which female cells lack, it will be even more problematic to produce them from women - many scientists even think this impossible without extensive genetic engineering.

This distraction would not much matter but for the way it is influencing debate about the Human Fertilisation and Embryology Bill. This new legislation, which reaches the Commons next month, will allow research into artificial gametes, while outlawing their use in fertility treatment. Such a ban is fine for now as this technology has not yet been developed, never mind proven safe. Scientists and patient groups, however, have proposed that Parliament should have a “regulation- making power” to approve clinical use in future with a vote, should evidence suggest it looks safe enough to try.

This would be a sensible measure. As the Bill stands, fresh primary legislation would be needed before patients could benefit, which could take years to reach the statute book. Yet the Government has so far rebuffed attempts to amend it, largely because of controversy about same-sex parents. If it were possible, the prospect of female sperm and male eggs would indeed be a proper subject for public consideration. But it is not, nor is it likely to be in the forseeable future, and the ethical questions raised have little bearing on helping the infertile to reproduce.

Mark Henderson is the Science Editor of The Times

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