Western Europe and the US

Spain used to give parents 2,500 euros (more than $3,000) for every newborn child to encourage families to reverse the country's low birth rate. But the checks stopped coming with Spain's austerity measures, raising the question of who will pay the bills to support the elderly in the years ahead.

It's a question bedeviling many European countries which have grappled for years over how to cope with shrinking birth rates and aging populations - and are now faced with a financial crisis that has forced some to cut back on family-friendly government incentives.

Spain and Italy, both forced to enact painful austerity measures in a bid to narrow budget deficits, are battling common problems: Women have chosen to have their first child at a later age, and the difficulties of finding jobs and affordable housing are discouraging some couples from having any children at all.

In 2010, for the fourth consecutive year, more Italians died than were born, according to the national statistics agency.Italy's population nonetheless grew slightly to 60.6 million due to immigration, which is a highly charged issue acrossEurope.

Italy's youth minister Giorgia Meloni said earlier this year that measures to reverse the birth rate require "millions in investment" but that the resources aren't available.

Unlike many countries in Europe,France's population is growing slightly but steadily every year. It has one of the highest birth rates in the European Union with around 2 children per woman.

One reason is immigration to France by Africans with large-family traditions, but it's also due to family-friendly legislation. The government offers public preschools, subsidies to all families that have more than one child, generous maternity leave, and tax exemptions for employers of nannies.

Like France, the United States has one of the highest population growth rates among industrialized nations. Its fertility rate is just below the replacement rate of 2.1 children per woman, but its population has been increasing by almost 1 percent annually due to immigration. With 312 million people, the US is the third most populous country after China and India.