There does seem to be a connection between the state of a local economy and the childbearing rates of its citizens. Populations increase with increasing prosperity in a developing society, at least at first. Fewer babies die, and more children live to grow up. Women are healthier, and thus more apt to bring healthy babies to term.
However, with more children surviving, and with employment opportunities increasing, the value of restraining reproduction begins to become apparent. Women start to bear fewer, albeit healthier, children.
As young people extend their educations and begin their life work later, reproduction is often postponed. This leads to a decline in fertility, because fertility in women drops fairly sharply with age. Many couples consciously choose to have fewer children or none, as they pursue the widening opportunities of a modern society.
Society begins to offer a variety of material rewards previously unavailable. Competition for these rewards encourages behaviors that free up disposable income for increased consumption. One of the most useful social behaviors, from the point of view of increasing consumption, is plainly smaller family size.
Therefore, population levels off, or at least the rate at which it is increasing slows. It may decline. Italy, among other European countries, has negative population growth right now. The USA would have negative growth, or close to it, if it were not for immigration. There would be too few workers coming up to pay for the present working generation's Social Security.
Paradoxically, reproduction levels remain high among some of those subcultures less caught up in the pursuit of new economic opportunities, those who for religious or social reasons do not join in the economic rise of the great mass. These groups still reproduce at high rates.
All of this assumes continuing economic growth and social progress. What if that does not happen? A look at modern Russia might help answer that question.
The USSR lost the Cold War. Its successor state, Russia, suffered for that loss. America may or may not have lost the peace, but in the early nineties, only Russia and her former satellites were in serious trouble.
Russia lost her political power, her military might, and her economic standing. There was, obviously, a pervasive social upheaval. There was horrible inflation, a sudden cessation of all subsidies, and many industries went bankrupt. Universal health care, such as it had been, disappeared. The decline in GDP was worse than that in America during the Great Depression, according to the Russian government. Those were miserable times, which the spirit of the people brought them through, and the economy has recovered somewhat. However, the question is: In the darkest days, what happened to Russian reproduction rates?
They plummeted. There were more deaths than births each year in post-Soviet Russia, and it is possible that there are still. In 2008 the death rate was 14.7 per 1000, while the birth rate was 12.1 1000. These figures are from an article in a blog called Sublime Oblivion titled Rite of Spring. The author, Anatoly Karlin, thinks the Russian population is already rebounding, and he is convincing.
It is possible that once a society has developed, population will decline with the economy and rebound when the economy rebounds. At least, there seems to be at least one state in which this is so. It is possible that a declining global economy will bring lower birthrates, and that these rates will rebound with the global economy. Yet as every family knows, reproduction is a complicated personal decision, not entirely dependent upon economic factors.