Infertility is normally seen as a private matter. If a couple are infertile and wish, they are not, that is sad. But there is understandable resistance in many countries to the idea that treatments intended to deal with this sadness—known collectively as assisted reproductive technologies, or ARTs—should be paid for out of public funds. Such funds are scarce, and infertility is not a life-threatening condition.

However, two papers presented to the "State of the ART" conference held earlier this month in Lyon argue that in Europe, at least, there may be a public interest in promoting ARTs after all. The low fertility rate in many of that continent's more developed countries means their populations are ageing and shrinking. If governments want to change this, ARTs—most significantly in-vitro fertilization (IVF)—could offer at least part of a way to do so.

As the conference heard, IVF does seem to be keeping up the numbers in at least one country. Tina Jensen of the University of Southern Denmark has just finished a study of more than 700 000 Danish women. She found that young women in Denmark have a significantly lower natural conception rate than in past decades. That is partly, but not entirely, because they are having their children later in life. The rest of the cause is unknown, though reduced sperm quality in men may be a factor. Whatever the cause, she also found that the effect has been almost completely compensated for by an increasing use of ARTs. Denmark's native population is more or less stable but some 3.9% of babies born there in 2003 were the result of IVF The comparable figure for another northern European country, Britain, was 1.5%.

Without IVF, then, the number of Danes would be shrinking fast. That it is not may have something to do with the fact that in Denmark the taxpayer will cover up to six cycles of IVF treatment. In Britain, by contrast, couples are supposed to be entitled to three cycles. In practice, many of the local trusts that dish the money out do not pay for any cycles at all. Jonathan Grant, the head of the Cambridge branch of the Rand Corporation (an American think-tank), believes this is shortsighted. His paper showed that if Britain supported IVF at the Danish level then its birth rate would probably increase by about 10 000 a year.

The cost of offering six cycles to couples (and doing so in practice, rather than just in theory) would be an extra £250 m-430 m a year. That is not trivial, but Dr. Grant reckons it is cheaper than other ways of boosting the birth rate. Some countries, for example, have tried to bribe women into having more children by increasing child benefits. According to this calculations, raising such benefits costs between £50 000 and £100 000 a year for each additional birth procured. Ten thousand extra births each year would thus cost between £500 m and £1 billion.

There are, of course, some disadvantages to promoting IVF In particular, women who use it tend to be older than those who conceive naturally, and that can lead to congenital problems in their children. But if the countries of Europe do wish to keep their populations up, making IVF more widely available might be a good way of doing so.