A global survey of fertility treatment covering more than 100 countries has revealed wide variations in international laws governing IVF, which are fuelling the growth of "fertility tourism".
At least 10,000 people go abroad each year to seek help to have a baby because the laws are too restrictive in their home country or the cost of treatment is too high.
No other field of medicine is subject to such wide differences in clinical practice, which are driven by social and religious attitudes rather than scientific evidence.
Experts at the World Congress on Fertility in Munich announced a code of practice on cross-border care, to be published by the European Society of Human Reproduction and Embryology (ESHRE) and the International Federation of Fertility Societies (IFFS) later this year.
Professor Ian Cooke, education director of IFFS, said: "What is considered acceptable varies from country to country. How carefully do they screen donors? How do they screen for multiple pregnancies? Do you want to come back with quadruplets? That's madness."
Both international organisations support the right of patients to go abroad. But they call for the harmonisation of national standards to increase safety.
In Britain, the chief reason for patients travelling is the shortage of egg donors, with waiting lists of up to two years in some clinics. Favoured destinations are Spain and the Czech Republic, where egg donors are paid €900 ($1600) and €800 respectively.
In Britain, regulations limit clinics to paying a maximum of £250 ($528) in compensation for lost earnings to egg donors.
Sperm donors are also in short supply in the UK, since donor anonymity was ended in 2005. Some couples travel abroad to obtain anonymous sperm. Cost is also a factor, with an average price of more than £3000 per cycle of IVF treatment in London. "It may well be cheaper to go to Barcelona or Prague and have a cycle of treatment there," Cooke said.
Dr Francoise Shenfield, co-ordinator of the ESHRE committee on cross-border reproductive care, said multiple pregnancy posed the biggest threat to patients. The UK restricts clinics to replacing at most two embryos in women up to the age of 40 but other countries allow up to four. Evidence shows multiple pregnancies carry higher risks for mother and babies.
"There is a striking difference between patients who had been abroad and those treated at home in terms of multiple pregnancies. Every clinic should have a strategy to reduce them," Shenfield said.
The survey revealed the rapid expansion of fertility treatment with more than 500 clinics in India and more than 600 in Japan.
