Birth rates decrease in response to exploitation either from people dying from your policies or people figuring out what's going on so they stop reproducing while you gloat about "replacing them" while telling
Birth rates are dropping all over the world due to women chasing carriers instead of family.
Japan is one to look at. Last time I looked, Africa is the only growing population,
And why this fascination with birth rates? Seems odd. Is birth rate a marker of a utopian society?