The effect of gradually lifting the two-child policy on demographic changes in China.

Low fertility rate has been a common problem in many industrialized countries. To reverse the declining trend of new births, Chinese government gradually lifted its restrictions on the number of births per family, allowing for a household to have no more than two children. Little is known about the additional births or population increase contributed by the gradual relaxation of birth restrictions. To fill this gap, this quasi-experimental design study including data from 124 regions used the synthetic control method and controlled interrupt time series analysis to evaluate differences in birth rates and rates of natural population increase between China and its synthetic control following implementation of the two-child policy (TCP) from 2011 to 2020. A total of 123 regions were included in the control pool. Data collected during 1990-2010 was used to identify the synthetic China for each study outcome. The mean rate differences of birth rates and rates of natural increase between China and synthetic China after TCP implementation were 1.16 per 1,000 population and 1.02 per 1,000 respectively. And these rate differences were distinguished from variation due to chance (one-sided pseudo-P-values: P for birth rates=0.047, P for rates of natural increase=0.020). However, there were statistically significant annual reductions in the pre-post trend of birth rates and rates of natural increase compared with those of controls of 0.340 less per 1,000 population per year (P=0.007, 95%CI = [-0.584, -0.096]) and 0.274 less per 1,000 per year (P=0.028, 95%CI = [-0.518, -0.031]). Results suggested that lifting birth restrictions had a short-term effect on the increase in birth rates and rates of natural population increase. However, birth policy with lifting birth restrictions alone may not have sustained impact on population growth in the long run.