China's ruling Communist Party announced Thursday that all couples will be allowed to have two children, ending the country's decades-old, unpopular one-child policy that has risked becoming a demographic burden as the population ages.

The one-child policy had been watered down several times since it was introduced in 1979, to the extent that most couples already qualified to have two kids.

Thursday's announcement officially removed all remaining restrictions limiting couples to only one child and signalled the country's desire to address the imbalanced sex ratio that has resulted from a traditional preference for boys.

Here are five things to know about the world's most ambitious population-control policy:

1. Why was the 1-child policy created?

China, which has the world's largest population at 1.4 billion people, introduced the policy in 1979 as a temporary measure to curb a then-surging population and limit the demands for water and other resources. It applied only to couples of the country's ethnic Han majority. Ethnic minorities were allowed more than one child, and five years after the policy was enacted, rural couples were allowed two children if their firstborn was a girl.

2. How was it enforced?

China's government has used a variety of incentives, coercions and punishments to enforce the policy. Even before the one-child regulations were introduced, the country tried to force couples to delay getting married until at least age 25 for women and 27 or 28 for men in cities, and 23 for women and 25 for men in the countryside.

China Forced Abortion

The one-child policy is often cited as the reason China has an estimated 32 million to 36 million more men than women — an imbalance the government has said it's worried about. (Associated Press)

Then, those who had only one child would receive "one-child certificates" entitling them to better child care, better housing, longer maternity leave and other benefits. Punitive measures were introduced for urban couples who flouted the policy. Their salaries were reduced by 15 per cent until the child reached age seven. In rural areas, couples who had too many children but couldn't afford to pay the fines reported that corrupt government officials would seize their furniture, motorcycles or other property.

China also hired more than one million part-time and full-time workers to ensure women used birth control and to encourage and harass them — some research suggests even force them — to get abortions, or to get sterilized, if they became pregnant with a subsequent child. Another technique was to deny anesthetic to women giving birth, to increase their aversion to getting pregnant again.

Over the years, the one-child policy has been eased. The major revisions came in 1984, when rural couples were allowed to have a second child, and in 2013, when any couple was allowed to have two kids if at least one of the parents was themself an only child.

3. Has it worked?

In 1979, when the one-child policy was introduced, China's population was just under one billion. The following year, the government projected the population would reach 1.2 billion by 2000, at which point the country would achieve its target of zero population growth. In actuality, China hit that number of people seven years too early, and its population now stands at a little shy of 1.4 billion and growing. However, the government estimates the one-child policy has prevented 400 million births and has helped lift countless families out of poverty by easing the strain on the country's limited resources. Many demographers counter that the birthrate would have fallen anyway as China's economy developed and education levels rose.

4. What problems has it caused?

Because of a traditional preference for baby boys over girls, the one-child policy is often cited as the cause of China's skewed sex ratio; the country has between 32 million and 36 million more men than would be expected naturally. Even the government acknowledges the problem and has expressed concern about the tens of millions of young men who won't be able to find brides and may turn to kidnapping women, sex trafficking, other forms of crime or social unrest.  

Multiple research studies have also found that sex-selective abortion — where a woman undergoes an ultrasound to determine the sex of her baby, and then aborts it if it's a girl — was widespread for years, particularly for second or subsequent children. Millions of female fetuses have been aborted since the 1970s. China outlawed sex selective abortions in 2005, but the law is tough to enforce because of the difficulty of proving why a couple decided to have an abortion.

The abandonment, and killing, of baby girls has also been reported, though recent research studies say it has become rare, in part due to strict criminal prohibitions.  

5. Why is China axing the policy now?

A communiqué from the Communist Party's Central Committee carried on China's official Xinhua News Agency said that the decision to allow all couples to have two children was "to improve the balanced development of population" — an apparent reference to the country's female-to-male sex ratio — and to deal with an aging population. United Nations projections forecast that, based on its citizens living longer and having fewer children, China will lose 67 million working-age people by 2030, while simultaneously doubling the number of elderly. That could put immense pressure on the economy and government resources.  

Repealing the one-child policy may not spur a huge baby boom, however, in part because fertility rates are believed to be declining even without the policy's enforcement. Previous easings of the one-child policy have spurred fewer births than expected, and many people among China's younger generations see smaller family sizes as ideal.


Key dates in China's family planning efforts: 

1953: Chinese leaders suggest that the population should be controlled and approve a law on contraception and abortion, but the plan is stranded by political upheaval and the 1959-1961 famine. 

1970: Chinese population exceeds 800 million. The State Council, China's cabinet, mandates sharp reductions in population growth rates throughout the 1970s.  

1975: China adopts the slogan "Later, Longer and Fewer" and urges urban couples to have no more than two children and rural couples no more than three. 

1979: The Communist Party introduces the one-child policy limiting couples of the Han ethnic majority to one child as a temporary measure to curb a surging population.   

1984: An adjustment of the policy allows a second child for many families in rural areas. 

2001: China decrees new laws to better administer the policy, including allowing local governments to impose fines for additional children. 

2006: Some provinces begin easing restrictions to allow couples who are both only children to have two children. 

2013: An exemption allows two children in families in which only one parent is an only child. 

2015: China's Communist Party says all couples will be allowed to have two children, but doesn't give a timeframe.

With files from The Associated Press