[ph0rque]

So maybe the way to reduce population growth is to make poor areas rich(er)?

[stratomorph]

Bingo, birth rate is a consequence, not a cause. He's trying to put the cart before the horse.

[electromagnetic]

Money is the greatest contraception. Being middle class typically makes people stress about money, so they worry they can't afford children, but they can freely afford condoms and the pill. The poverty striken can't necessarily afford condoms/pill when they want to have sex.

The middle class is being sexually out performed by the poor and the rich.