Data analysis
Descriptive analyses were performed to compare the maternal and fetal demographic and outcome variables for the three groups: land, water, and WWI-only births. For some analyses the water birth and WWI groups were combined into a single group (highlighted in the text below). Data are presented using median and inter-quartile range (IQR) for continuous data (due to skewed distributions), frequencies and proportions for categorical variables. Chi-square tests were performed to investigate associations between the groups (land, water, WWI) and categorical variables (e.g., NNU admission, perineal damage). Chi-square tests and Mann-Whitney U-tests were used to look for associations between NNU admission and maternal variables. Multivariate logistic regressions were used to model the odds of NNU admission, where variables were selected for inclusion based on their clinical relevance. These models contained the following variables: birth group (WWI vs waterbirth vs land birth; maternal age, maternal BMI, previous birth mode, epidural use, length of labour (1st + 2nd stage) and labour onset. All analyses were performed in R (version 4.0.2).