BEIJING, Jan. 6(Xinhuanet)-- The birth of the boy officially declared to be the 1.3 billionth Chinese citizen at 12:02 Thursday morning prompted some to examine China's tremendous achievements in population control and the challenges to come.

More than three decades ago, the Chinese government adopted a family planning policy to rein in the country's runaway growth in population. Demographers hold that if it were not for the policy, the 1.3-billion population would have come in China four years earlier.

After more than 30 years of exertions, China has shifted its population reproduction from a high-birth-rate against low-mortality to a low-birth-rate against low-mortality pattern.

Official data show that in the early 1970s, a Chinese couple had 5.8 children on average. That number has dropped to 1.8.

The achievements were accompanied by a string of demographic challenges to the Chinese economy and society, however, and the ensuing demand for readjustment of the nation's population policies, demographers say.

They cite the aggravating gender imbalance, increasing transient population and related education, advent of an aging society and mounting employment pressure from soaring labor population.

Yu Xuejun, director of the policy and regulations department of the State Population and Family Planning Committee, said that the years up to 2015 would be the most critical period for population growth in China.