Strengths and Limitations
To our knowledge, this is the first systematic review to identify key outcomes reported in studies evaluating planned mode of birth. The strengths of the present study include its comprehensive search strategy and methodological design following methodology of previous publications in this field 12, 23. To prevent bias in the review process, study selection was conducted independently by two researchers and discrepancies were resolved through discussion. However, the exclusion of retrospective studies and strict inclusion criteria meant that certain useful reported outcomes may have been omitted. Whilst it may be useful to review retrospective trials, the outcome selections in retrospective trials could be influenced by many factors, including finances and time frame, and tend to have reporting bias, therefore affecting the quality of outcomes and outcome measures selected. The high prevalence of reporting bias could have an impact on the conclusions in Cochrane reviews 24. Given that up to 85% of studies are wasted throughout various stages of research, accumulating a loss of tens of billions of dollars of investment in research annually, improved methodological input for research design at an early stage, such as selecting appropriate outcomes, is detrimental25.