It has been argued but not proven that more-prosperous societies have lower birth rates, and people saying that point to Mexico's falling birth rate. Middle-classness, it is said, cuts off the poor person's drive to have many children -- which is, after all, partly an economic impulse.
In 18th-century and early 19th-century America, when pregnancies abounded, large families ensured many hands to do the farm labor and help ease later life for the parents. It was not uncommon for a traveler to be met, at the door of a back-country cabin, by a woman with nine children. "Poor man's Social Security" was invented eons ago. Prosperity eclipses that drive.
Infanticide and the Tophet were resorted to by people who feared they had too many children to feed -- or who feared that too many heirs would cause dissension and a relapse back into poverty for the family, when the family "nut" was divided up below the critical mass needed for investment income. That, it is said, is why the Phoenicians (and following them, the Carthaginians) began to "sacrifice" children to their gods, even at the expense of blackening their national name forever.
Augustus Caesar sure thought that debauchery sapped the virtue of the upper class, his daughter being a case in point. BYW, the period from 1715 onwards saw a huge spike in the growth of the British colonies in North America. A large part of this was the rate of natural growth among both whites and blacks. The highest birth rate in our history, I think. The population was becoming acclimatized to the savage Anerican climate, and there was plenty of food. A growing and prospering population has a different dynamic than a stagnant one. The Indians were the only ones suffering—from diseases they could not overcome, but even they profited from the much increased trade. So, one can say that a population boom was a cause of the Revolution, because people were spilling over into the Ohio Country. George Washington are very, very aware of the dynamic—unlike many of the other Founders,and he was always acting on it. One of his great efforts wss to connect the Potomoc Valley with the Ohio Country. Only the lack of emgineering talent—and capital—and the terrain kept him from his goal. A very entrepeneurial spirit, Mr. Washington. Not until Jackson did we get such an expansionist minded President, although we have to give Jefferson credit. But unlike Washington or Jackson, he was not very physical in his efforts.