BEIJING, Dec.21 -- All couples in China are encouraged to have two children, according to a draft amendment to China's national law on population and family planning proposed to China's top legislature for review on Monday.

China's top leadership announced the universal two-child policy at a meeting in late October, but it has to be approved by the National People's Congress before it becomes law.

It is widely expected that the draft revision could be passed when the legislature closes its biomonthly session on Sunday.

The draft, proposed by the State Council, China's Cabinet, to the National People's Congress for review, said couples who have two children can enjoy longer maternity leave. It also said couples could have more than two children if they are eligible.

The draft said the two-child policy would come into force on Jan 1.

Relaxation of the family planning policy is expected to provide part of the solution to the challenge of an aging population, and to become a new driver for the economy in the long run.

By the end of 2014, the number of people over 60 years of age had reached 212 million, accounting for 15.5 percent of the total population. Of those, about 40 million were disabled or partly disabled.

The new two-child policy could increase economic growth rate by 0.5 percentage points through reducing China's dependency ratio, said National Health and Family Planning Commission in November.

The change in policy is expected to mean over 30 million more people in the labor force by 2050 and an decrease of 2 percentage points in the share of elderly of Chinese population, said Wang Pei'an, deputy head of the commission.

The draft also forbids surrogacy in any form, and forbids buying or selling of sperm, eggs, fertilized eggs and embryos. It allows authorized medical institutions to conduct assisted reproductive procedures after approval from provincial-level health authorities.