Wealth and fertility have an inverse relationship. This is true worldwide, and through recent history (~50 years). Just one of many reasons, women are going to college and having careers at historical highs. And the same women are punished for having kids.
"This decreasing relationship between fertility and income is well known to economists and demographers alike. In addition, it holds true over time: Rich countries, such as the U.S., have experienced a remarkable decline in their fertility rate as they became rich. Also, the relationship holds at the individual level, as rich families tend to have fewer children than poor families." from: https://www.stlouisfed.org/on-the-economy/2016/december/link...