China's "family planning policy" restricts most urban couples to one child, and rural couples to two.
Since China introduced the family planning policy in the late 1970s, it’s estimated to have prevented adding 400 million people to the current population. That more than the entire population of the United States.
China’s birth rate in 2012 dropped to 12 per thousand from the 33 per thousand in 1970. As a result the population growth rate has declined to one-fifth of what it was in 1970, and only half of the world average.