Data extraction
Two reviewers (X.L.L and H.Q.L) independently extracted the relevant data from the eligible articles using standard forms. The data extracted included information about the first author, the year of publication, country, study setting, study design, type of participants, age of study participants, overall sample size, scales used to ascertain traumatic birth or PTSD, time of traumatic birth/ PTSD ascertainment, and the number of events (trauma birth and PTSD). Two reviewers resolved discrepancies through discussion, and any disagreements between the two reviewers were resolved by the third reviewer (R.H.X).