Well, in large part because of draconian measures that China and other countries have taken, measures that include mass sterilization, forced abortions the toleration of female infanticide. While staying a millimeter away from putting its stamp of approval on these tactics, The Economist proclaims that "it has worked" and is benefitting all of us by making maternity wards almost obsolete in some places.
I couldn't help but be reminded of this verse:
And just think, if it weren't for many of us families who have more than 2.1 children, the world would be an even cleaner, more educated, more enlightened, more sophisticated place where the few people left could enjoy life without pollution, hunger, global warming, crime, disease....and grandbabies.
Falling Fertility Makes for Happy Economists