China implemented a one child policy in 1979 to control its rapidly growing population of over 1.3 billion people which comprised 20% of the world's population. The policy restricted couples to only one child and imposed fines for additional children. It succeeded in significantly reducing the birth rate from 31 to 19 births per 1000 people over 20 years, avoiding an estimated 230 million more people. However, later the replacement rate declined too much, so exceptions were made to the policy to increase births and ensure future population replacement.