Fig. 2

The selection flowchart of participants. The data was collected from Hebei Maternal Near Miss Surveillance System, which involved 22 hospitals in Hebei Province, China. There were 167,601 parturient who gave birth in these hospitals from January 1, 2015 to December 31, 2017. Women with ≥20 gestational weeks, singleton pregnancies were included. Total 116,042 parturients were included in this study