You say "yet" but "and" would be more appropriate. The fertility rate is a symptom of, among other things, high child mortality and low access to birth control.
and religion. We need to face the fact that religion, often religion exported by the west, is killing people in these countries. Almost all missionary religions forbid birth control.
Protestant Christianity typically doesn't forbid birth control, as far as I know.
Evangelical protestant Christianity does. And the other forms of protestant Christianity rarely travel to Africa and other third world nations on mission trips.