2.3. Quality assessment and data extraction
Data extraction was independently completed by LB and LM
using a prespecified data extraction form. The following data were
extracted from the selected studies: (1) methods of study
(including study design, data collection and time-period of the
study); (2) characteristics of trial participants (including number of
participants, setting and country) and the inclusion and exclusion
criteria; (3) type of intervention (VD versus CS); (4) type of
outcome measures (perinatal and/or neonatal mortality, secondary
outcomes); (5) statistical methods.
To ascertain the validity of eligible observational studies, the
reviewers independently determined the adequacy of inclusion
and exclusion criteria, characteristics of study participants,
inception cohort, selection bias, interventions and co-interventions,
outcome measurement, confounders, subgroup analyses and
follow-up.
To explore the heterogeneity in study results the following
hypothesis was specified before conducting the analysis. The
reviewers hypothesized that the intention for the individual
interventions (CS or VD) may differ in the studies leading to
confounding by indication.