Once you hit ~1.5 TFR, low fertility trap kicks in.

> Demographers in the early 2000s coined the “low-fertility trap,” hypothesizing that a series of self-reinforcing economic and social mechanisms make it increasingly difficult to raise the fertility rate once it dips below a certain threshold. The academics posited that lower fertility results in increased individual aspirations for personal consumption but at the same time it also results in an aging population and less job creation—and thus greater pessimism about the economic future—which in turn disincentivizes having more children. Moreover, as the average family size grows smaller and smaller generation after generation, the social norm of an ideal family size shrinks, too. These forces together lead to a persistent “downward spiral” for the fertility rate that can be impossible to reverse.

> China’s not the only country in the region or the world facing this kind of demographic crisis. Fertility rates across developed nations globally have almost uniformly dropped over the last few decades. China’s neighbors Japan and South Korea have among the lowest, and policymakers there have invested billions of dollars and pondered uniquely targeted policies, respectively, to try—so far unsuccessfully—to get young people to have more children.

https://time.com/6306151/china-low-fertility-trap-birth-rate...

https://onlinelibrary.wiley.com/doi/10.1111/j.1728-4457.2005...