Characteristics of included studies
This systematic review included one cohort study[22] and eight cross-sectional studies[23-30] with 3,821 postpartum women. A total of 1,823 with traumatic birth and 353 with postpartum PTSD were included in the final analysis. The included nine studies[22-30] were conducted in Turkey, the United Kingdom, Iran, Serbia, Australia and the United States and published between 2003 and 2020. The overall sample sizes ranged from 77 to 950, the number of traumatic childbirth and PTSD respectively from 15 to 675 and from 2 to 127. For the assessment scales for birth trauma, five studies[22,24,26,28,29] used DSM-IV/V A criterion, three studies[26,28,30] were based on maternal self-report and one study[23] was unknown. For the evaluation time of traumatic birth/postpartum PTSD, six studies[22,25-28,30] were within the 4-8weeks after birth, one study[29] was at postpartum 1-4months, one study[24] was at postpartum 1-12months , and one study[23] was unknown. Two types of scales for screening PTSD were used in eligible studies[22-30], including structured interview diagnostic scales and self-assessment scales. Of them, seven studies used PTSD assessment scales[22-24,27-30] that belonged to the self-assessment scale, including Post-traumatic Diagnostic Scale (PDS)[22,23,27], Trauma Experience Survey (TES)[24,28], Post-traumatic Stress Disorder Checklist for DSM-5 (PCL-5)[29], Post-traumatic Stress Symptom Scale-Self-report (PSS-SR)[30]. And one with the Post-traumatic Symptom Scale-Interview (PSS-I) [25] and one with the Clinician-Administered PTSD Scale (CAPS) [26], which were classified as structured interview diagnostic scale. The characteristics of the included studies are showed in Table 1.