China has some of the lowest birth rates in the world; as a whole, the rate hovers around 1.8 births per woman, although some experts estimate it's actually closer to 1.5 -- and in areas such as Beijing and Shanghai, the rate drops to 0.7 [source: LaFraniere]. Thirty years ago, though, these numbers looked much different. The fertility rate then was 2.9 children per woman and looking even further back, in 1970 China averaged 6 children born to every woman [source: Hesketh].
The modernization of China, including urbanization developments in the 1970s that drove cost-of-living increases as well as rising education levels, may be playing a role not only in its economic growth but also in its low birth rates, suggest some. But it's not the only thing. Also beginning in the late 1970s, China began encouraging the ideas of "late, long, few" -- voluntary family planning by delaying marriage, having fewer children and increasing the number of years between children. In 1979, the government introduced and implemented its formal one-child policy, an aggressive effort to improve standards of living and the economy through population control. Although the government originally planned for a short-term program, the successful prevention of about 400 million births lead China to keep a revised version of the policy in place ever since in an effort to keep population growth under strict control [source: CNN].
Under the one-child policy, urban couples (roughly 680 million of China's population lives in cities) aren't allowed to have more than one child; overall about 63 percent of all Chinese couples fall under the one-child rule, and most are Han Chinese [source: LaFraniere].
Exceptions are made only for couples who fit certain limited criteria. Before having a child, Chinese couples must apply for permission, called a birth permit. In rural areas, couples may apply a birth permit to have a second child if their firstborn is a girl, and couples are allowed three children if they are of an ethnic minority. China also relaxes its policy for any couple who themselves grew up as only children, whether one or both of the pair is a singleton, allowing these couples to have up to two kids. Additionally, any couple whose child is disabled or killed in an accident may be allowed to apply for a second birth permit (or to adopt). The deadly 8.0 magnitude earthquake that hit the Sichuan province in May 2008 killed an estimated 10,000 children and left thousands more severely injured, disabled or orphaned -- and is an example of a circumstance that allowed couples to have second children.