Statistical analysis
We used Microsoft Excel and R for Windows version 4.1.1.(32). Descriptive statistics (i.e., frequencies and
percentages for categorical data) were used and no data were imputed as
missing data was negligible (<5%). Trends over time in mode
of birth and perinatal outcomes were depicted in graphs. For all
perinatal outcomes we excluded the cases with stillbirth or unknown
moment of death.
Since our data are population-based rather than a sample that requires
extrapolation we present our data as absolutes and percentages without
statistical analysis.