In Asia, it has likely happened already.

In the poster boy of overpopulation, Bangladesh, the fertility rate dropped from 6.2 children to 2.1 children per mother (https://www.ft.com/content/f60e2ddc-0bbc-11e1-9861-00144feab...). No Asian country today has fertility rate above 2.5 AFAIK (except maybe the Philippines).