How much can governments do to boost birth rates and avoid population ageing? A lot of research is going into encouraging higher fertility, but demographers are still perplexed. In the Vienna Yearbook of Population Research 2008, John Bongaarts, who has worked with the Population Council in New York for 30 years and is one of the world’s most respected demographers, tackles the question. And his answer is: not much.

In most countries, there is a gap of about 0.8 to 0.9 births between the number of children that women have and the number that they want to have. Economic factors account for perhaps 0.2 or 0.3 births per woman. So creating ideal economic circumstances will not achieve a miraculous increase in fertility. Furthermore, no government policy will eliminate all economic obstacles, so the increase which can be achieved is very small indeed.

Social obstacles to fertility also exist. However, governments are reluctant to interfere with women’s lifestyles. Japan and Singapore have attempted to raise marriage rates amongst young women, but they have had very little success. Biological obstacles to fertility seem to be increasing because women are marrying at a later age and are then finding it difficult to conceive. So Bongaarts feels that IVF could play a role in increasing fertility.

What Bongaarts highlights is what he calls "tempo changes", or decreasing the age at which women bear children. This accounts for about 0.25 births per woman. He says "if a country could manage to turn around an upward trend of 0.1 years per year in the mean age at childbearing and initiate a slow decline of just 0.1 year per year, the period TFR [total fertility rate] would increase by 20 per cent." Furthermore, childbearing at a younger age decreases the biological obstacles, as well. His colleagues are excited about this idea, too – but he fails to make any practical suggestions about how to make it happen.

So, if governments want to increase birthrates, the number of factors becomes bewilderingly large:

"A comprehensive pronatalist policy should focus on all factors that cause actual fertility to be lower than the ideal level, not just economic ones. This means going beyond conventional economic measures that reduce the costs of childbearing and considering efforts to reduce biological and perhaps even social obstacles to childbearing. In addition, policies aimed at reducing or reversing the tempo distortion can have a substantial impact without requiring significant changes in behaviour."

This all sounds optimistic but in the end Bongaarts acknowledges that it is basically just academic theorising:

"It appears that with a comprehensive policy and a substantial commitment of resources, fertility can be raised by a few tenths of a birth per woman above the level that would prevail without these policies. Effective tempo policies could result in even larger effects in the short run. Such effects would bring about a substantial reduction in the rise of the old-age dependency ratio by 2050, but would fall well short of halting population ageing. Nevertheless, the challenges posed by population ageing are so critical and so difficult to address that any step in the right direction is beneficial."

In other words, using every tool available, governments may be able to increase the number of children being born by a bit – but just a little bit. And nothing they do will stop population ageing.