“There are no families with many children in this area anymore — they all have one or two,” says Hasibe Enc, who lives in the small, affluent city of Urla in western Turkey. That is irksome for her, since she runs a kindergarten called Pink Dreams. But it is also a crisis for Turkey — or so the national government believes.

Although it is the youngest country in Europe, Turkey is no longer delivering enough babies to sustain its population in the long term. Recep Tayyip Erdogan, its president, rails against abortion and tells women to bear at least three children. To sweeten these vinegary exhortations, the government is introducing “birth aid” payments for each baby born to a citizen and longer parental leave for civil servants.

In Singapore, couples receive $4,450 for having one child, another $4,450 for a second child and about an additional $6,000 for a third. Families with babies go to the front of the queue for government housing, in which most Singaporeans live. In South Korea, the state reminds lovers that they can marry cheaply, without throwing an expensive wedding. In Russia, couples are encouraged to get it on for the sake of the motherland on an official “fertility day”; a patriotic woman who gives birth exactly nine months later might be entered into a raffle to win a car.

In every rich country except Israel, the total fertility rate (a measure of births per woman) is below 2.1 — the level required to keep the population stable. In Japan it is 1.4. Some not-so-rich countries, including China and Russia, are also below the replacement rate. Singapore watches its fertility the way other countries track their balance of payments. Mathematically, that is foolish. But it is understandable: Singapore’s fertility rate is just 1.2. South Korea’s is no higher.

A country that worries about having too few young people to pay old folks’ pensions might be able to import workers. But that tends to bring the natives onto the streets. And homegrown citizens are handy for conscripting into armies. So, as birthrates decline, more countries are turning pro-natalist (not long ago, Iran and Turkey worried that their populations were growing too fast and handed out free contraceptives). And the baby-boosting is becoming fervent, even desperate.

The trouble with babies is that costs and benefits are misaligned. Couples must pay for them directly, in the form of clothing, extra bedrooms and school fees, as well as indirectly, by cutting back on paid work to look after the little horrors. In Europe, a single child is reckoned to cost 20 percent to 30 percent of household income. Parents get scant economic return on this investment. Their children might help them in their dotage but are rarely forced to do so by law in the way that parents must care for their children. Some of the fruits of their children’s labor, which they might reap, are instead taken in taxes.

Almost all pro-natalist policies try to improve this dismal deal by introducing a third transfer, from the state to parents. This might be a per-baby lump sum or an ongoing child-benefit payment. It might be generous paid leave or subsidized nurseries — Nordic countries tend to offer both. It might be child tax credits or tax breaks. The last measure particularly encourages high-earners to have children, which might be good for the exchequer but is hard to defend politically. Francois Hollande’s government has pruned France’s once-generous tax breaks for parents.

At least in the rich world, the more governments spend, the more they seem to get. Nordic countries shell out the most and are rewarded with more babies; stingy Mediterranean countries have the fewest babies in Europe. The causation may not be all one-way, of course.

Yet not all state baby bribes are equal. “The kind of spending matters more than the amount,” says Olivier Thévenon, who tracks natalist policies at the OECD, a club of mostly rich countries. Longer maternity and paternity leave are nice but seem not to encourage childbearing. Cash payments and gifts encourage couples to have babies more quickly but not to have more than they otherwise would.

The clear winner, according to Thévenon’s research, is subsidized child care. Decent, affordable nurseries make it easier for women to combine work and motherhood.

In countries such as Turkey, the problem is less cash than culture. Ask Turkish women about work and motherhood, and the response is a torrent of grievances. Husbands do little housework. Grandparents are too far away to help much, and lack energy — a consequence of older parenthood. Employers are unsympathetic. In short, mothers are generally still expected to stay at home, says Nigar Goksel of the International Crisis Group, an NGO. Until that changes, Turkish women will perceive a sharp choice between work and parenthood and often plump for the first.

In East Asian countries such as Japan and South Korea, the expectations heaped on wives and mothers are even harder for educated women to bear. Working hours are so long that it is almost impossible to combine work and any active parenting role. Children must also be tutored for make-or-break exams, raising the cost of child-rearing. And, unlike in Western Europe or Scandinavia, women must sign up for the whole wife-mother package: Births outside marriage are rare..

In many countries, fertility is highest in rural areas, middling in small towns and suburbs, and lowest in the cores of large cities. Though it may be hard to believe amid all the Bugaboo prams and bulging primary schools, inner London has a fertility rate of 1.5, compared with 2.0 in outer London. Of course, many people move to suburbs and small towns to have children. But research on Britain and Nordic countries shows that the discrepancy remains even when you account for the people who move.

It might be that property prices in city cores have risen so high that urbanites feel they cannot afford to allocate space to children. It might be that the amenities of spruced-up inner cities are now so great that the opportunity cost of childbearing (all those nice restaurant meals forgone) is intolerably high. It is also likely that emerging patterns self-reinforce. People living in suburbs with lots of babies are encouraged to have babies; people in childless areas are more likely to skip procreation entirely. “Fertility is contagious,” says Hill Kulu of Liverpool University, an expert on this matter.

The Japanese government is convinced that big cities are actually causing infertility and wants to prevent young people from moving to them. Economically, that is loopy: People are more productive in big cities. But if the prescription is wrong, the analysis might not be. It could be that a combination of urban redevelopment and restrictions on housing supply have created streets that are lovely, wealthy, exciting — and childless.

Copyright 2013 The Economist Newspaper Limited, London. All Rights Reserved. Reprinted with permission.