This is unrelated to standards of living, or "overpopulation," (which is always thinly veiled racism).
You can lower the teen birth rate just by giving kids access to contraception, teaching them about sex education, that they are in control of what happens to their own bodies, that some youth pastors are creeps, and most importantly, that they can choose to be a wife and have kids, or, they can just... choose to not do any of that, and it's all fine either way. Choice.