Statistical analysis
The incidence of metabolic acidosis varies between 1.3% to 5.7% and the confidence intervals are very wide. For this reason, no power calculation was conducted for this study. Based on the study of Wiberg-Itzel et al ., a sample size of 3000 women was chosen to achieve a sufficiently large number of the predefined outcomes for the calculations in a reasonable timeframe (9).
Receiver Operating Characteristic (ROC) curves with the respective areas under the curve (AUC) were calculated for the relevant outcomes. Spearman rank correlation coefficients were calculated. Kruskal-Wallis or Fishers exact test were used when appropriate. To investigate a possible relationship between the discrepancies in values obtained by either the two BGAs or POCs linear regression and one sample T-test before a potential Bland-Altman plot was constructed. Analyses were performed using SPSS 26.0 (SPSS, Chicago, IL, USA). For the calculation of sensitivity, specificity, positive (LR+) and negative likelihood ratios (LR-), with their 95% confidence intervals, Medcalc.org was used.