Background: In January 2016, China ended its 35-year-old one-child policy and replaced it with a nationwide two-child policy. However, it remains unclear whether a two-child policy can effectively increase the fertility level in China.

Objective: We reviewed the 30-year (1985–2015) two-child policy experiment carried out in Yicheng, a county in the Shanxi province of China, to assess the impact of this policy on the crude birth rate, as compared with the one-child policy implemented in most other places in Shanxi.

Methods: We adopted a synthetic control approach. Using this method, we constructed a synthetic county using counties in Shanxi that were subject to the one-child policy. The synthetic county had similar observed characteristics to Yicheng before the launch of Yicheng’s two-child policy experiment in 1985. Therefore, birth rate differences between Yicheng and the synthetic county after 1985 could be attributed only to the two-child policy.

Results: We did not find any short-term impacts of the two-child policy on the Yicheng birth rate prior to the 1990s. We estimated that the two-child policy, in the long run, would lead to a maximum of two more births per 1,000 people every year in Yicheng, compared with similar areas that had a one-child policy.

Conclusions: The two-child policy was not found to boost the birth rate in Yicheng and similar places.

Contribution: The study identified the causal effect of a two-child policy, and was more methodologically reliable than related studies that primarily explored statistical correlations.