In China, the adjustment of the family planning policy was expected to increase the number of births and trigger a change in the demographic and obstetrical background of pregnant women. The policy itself, and corresponding background variations of the pregnant mothers, might have various influences on certain birth-related characteristics. Moreover, the adaption of the medical system to the policy needs to be demonstrated. To address these issues, over 50,000 individual records from January 2012 to December 2018 were collected from a large tertiary care centre of southwest China as a representative. The monthly numbers of deliveries and births showed stabilized patterns after remarkable upward trends. Policy-sensitive women, among whom older age and multiparity were typical features, contributed considerably to the remarkable additional births. Indeed, multivariable logistic regression analysis identified the child policy and these two background characteristics as factors influencing CS (caesarean section) rate and certain pregnancy complications or adverse outcomes. After the implementation of the two-child policy, a care provider was faced with fewer but more difficult cases. Briefly speaking, more individual-based studies on family planning policy and more efforts to improve obstetrical service are needed to better guide clinical practice in the new era.