Here's some interesting information I picked up in, of all things, an Environmental Biology class:

It seems that, in technologically ascendant nations such as the United States, population growth is actually slowing over time. In Italy in particular, zero population growth has already been reached, and it currently experiences fewer births than deaths. The growth still continues to skyrocket in less affluent nations, and I would presume in less affluent portions of the rich nations (there are certainly inner-city areas where the average family size is much greater than national), but as the world's population gets (in general, and very slowly in some areas, due to various processes too complex to get into here) richer, it would mean that the overall population growth would slow as well, eventually stabilizing at zero population growth, at around the seven-to-twelve-billion people range according to the information I received in class.

Reasons for this include people generally having better access to methods of birth control in more affluent nations, being more familiar with the dangers and responsibilities of having large families, infant mortality rates are now lower so couples feel less compelled to have many children so that at least a small number will reach adulthood, there are plain out fewer couples since more never marry, with pressures of career and other concerns weighing more heavily on them, and, importantly, and don't laugh, they are more likely to have better things to do that to produce offspring.

China, with its unique combination of low per-capita income and enormous population, has passed laws, to some success, to try to curb its growth. But throughout much of the industrialized world (and now, I suppose, the "informationalized" world), birthrates have fallen to below China's current, state-mandated limits.

As a result, world population growth rates are starting to decline, and in fact a contrary problem has arisen: with the demographic spreads of many nations tending to become elderly-heavy, how can the younger generations hope to support them?

Searching the web for information to substantiate this odd class-learnt fact, I found: