Data extraction and management
Two researchers (HWL, ELT) independently screened titles and abstracts, and subsequently reviewed the full text of each selected study to assess for eligibility. Any discrepancies in initial screening between the two researchers were resolved by discussion with a third author (MB). The following data were extracted from the selected studies: participant demographics (sample size, age, geographic), study design, interventions (spontaneous vaginal delivery (SVD), operative VD, planned/ elective CS or unplanned/ emergency CS), primary and secondary outcomes, outcome measures and definitions (if given). If the primary outcome was not stated explicitly, the main outcome reported in the conclusion or the outcome included in the study’s power calculation was recorded. The authors of the studies were not contacted to clarify the details of primary outcome. The composite outcomes were recorded in the extraction of outcomes.