Statistical analyses
Distribution of data was analysed using the Kolmogorov-Smirnov test. Normally distributed data are expressed as mean ± standard deviation. Not normally distributed variables are expressed as median and minimum-maximum. Categorical data are given as counts (n) and percentages (%). Continuous data were compared with paired t-test and Wilcoxon signed-rank test, respectively. Categorical data were compared with Chi2 and Fisher’s Exact test, respectively, with a 99% Confidence Interval (CI). Nonparametric receiver operating characteristics (ROC) analysis was performed to predict the prognostic power of the risk score and to generate a cut-off value that discriminated best between the event of stillbirth versus live birth. Odds ratio (OR), as measure of the relative risk of stillbirth, was estimated using logistic regression analyses with a 95% CI. All reported p -values are two-sided, and level of significance was set at <0.05. Statistical tests were performed and figures created by SPSS® Statistics Version 26.0.0.0 (IBM Corporation ©, Armonk, NY, USA).
The study was approved by the Ethics Committee of the Medical University of Vienna (EK 1759/2018 ) and complied with the principles outlined in the Helsinki Declaration of 1975, as revised in 2013. Patients’ written consent was not required as per Austrian Federal Act concerning Protection of Personal Data (DSG 2000).