China Since 1968
In 1968, China was one of the poorest nations in the world, in per capita GDP ($671 in inflation adjusted dollars). Only Rwanda and Malawi were poorer. It also had one of the world's highest fertility rates. Fertility began to decline sharply in that year, from 6.37 in that year to 2.8 in 1979, the year the one child policy was introduced. By 1993 it had reached 1.87, well below the replacement rate, and has remained below it ever since. Note that most of the decrease occurred before the "one child" policy was introduced. Per capita GDP increased relatively slowly during the eleven years while fertility was declining to 2.8, but accelerated sharply thereafter, and had increased 25 fold (2518%) by 2018. Note that all the fertility decline occurred while China was still a very poor country, and that nearly all of the rapid economic progress happened after fertility had dropped to low levels.
I have included a graph with a trace of Chinese GDP per capita vs fertility since 1968. Those who wish to explore on their own may click on this link.