FAMILY planning has been a huge success. The global fertility rate has crashed, from 5.1 babies per woman in 1964 to 2.5 today. The average Bangladeshi woman can now expect to have about the same number of children as the average Frenchwoman. Only in sub-Saharan Africa are big families still in vogue, and even there they are shrinking. This is welcome. It suggests that women have gained more control over their bodies and that parents no longer reproduce frantically for fear that some of their children will die. Cutting the birth rate also leaves countries with fewer dependants per worker, at least for a time, making them better off.

But this triumph conceals a growing problem. For more and more couples, the greatest source of anguish is that they have fewer children than they want, or none at all. With Globescan, a consultancy, The Economist polled 19 countries, asking people how many children they would like and how many they expect to have. In every rich country we surveyed, couples expect to be less fertile than they would like, and many in developing countries suffer the same sorrow (see article). On average, Greeks think the ideal family contains 2.6 children but believe they will end up with 1.7.

Medical infertility is part of the problem, not just in rich countries, where couples put off having children until it is rather late, but also in poor countries, where health care is worse. By one global estimate, at least 48m couples have been trying for a child for the past five years but have not succeeded, up from 42m in 1990. But the main reason for the shortfall, according to our poll, is money. From Brooklyn to Beijing, the cost of housing and education is so high that many young people say they cannot afford as many children as they want.

Malthusians will rejoice. The population is growing fast enough already, they will argue. Besides, can’t infertile couples just adopt children? In fact, population growth today largely reflects longer lives and will eventually go into reverse. It is not clear that there are too many people; and it is callous to ask couples who might want children to forgo that joy simply because some of their neighbours would prefer a less populous planet. And adoption, though admirable, is neither the sole responsibility of the childless nor a perfect substitute for procreation.

The pain of having no or fewer children than you desire is often extreme. It can cause depression and in poor countries can be a social catastrophe. Couples impoverish themselves pursuing ineffective treatments; women who are thought to be barren are divorced, ostracised or worse. Last month a childless Kenyan tailor was charged with attempted murder, having allegedly attacked his wife with a machete.

More frugal innovation, please

In wealthy countries, where maternity wards are quiet partly because the young are so economically insecure, governments can help by doing things they should be doing anyway: liberalising labour markets that shut the young out of jobs, relaxing planning rules to make housing cheaper and promoting child-friendly policies in the workplace. Across the world, education is important, both to warn women about how fertility declines with age and, especially in Africa, about preventable infections such as chlamydia and gonorrhoea.

Most important, however, is medical innovation. In vitro fertilisation (IVF) has become better over the years but is still horribly expensive. Some couples remortgage their homes in the hope of conceiving. Research into more frugal technology is staggeringly rare, given the demand for it. Would lower, cheaper doses of IVF drugs work as well for some people? No one knows. Will a shoe-box-sized IVF laboratory developed in America work reliably? Trials are only now under way.

More money for research would help, as it generally does. But perhaps not as much as more attention. Governments and aid agencies have turned family planning into a wholly one-sided campaign, dedicated to minimising teenage pregnancies and unwanted births; it has come to mean family restriction. Instead, family planning ought to mean helping people to have as many, or as few, children as they want.