Estimates of inpatient admission rates and associated costs for infants before and after China's universal two-child policy

China implemented a universal two-child policy in 2015. It is important to understand infants' medical utilization in the context of this policy to inform health policies and resource allocation. This study utilized a 20% random sample of administrative data from China's Urban and Rural Basic Medical Insurance (URBMI) in one of the largest southern Chinese cities from January 2015 to June 2018. Ordinary least squares models were used to estimate changes in inpatient admission rates and costs for infants between 0 and 6 months old after the implementation of China's universal two-child policy. The overall inpatient admission rate was 27.2% in 2015 and 31.3% in 2017. Compared with 2015, there was an increase in inpatient admission rates for infants 1 month old or younger (coef = 0.038, 95% CI = 0.029 to 0.047, p