Statistical analysis

Demographic data are presented as median (IQR) or N (%), and the difference between the five groups was assessed using Kruskal-Wallis's test for continuous variables and Fisher's exact test for categorical variables.

Linear mixed models with random intercepts to account for variation between women and to correct for dependence between different measurements from the same woman were used to investigate gestational changes of VPT and VI at the three IJV locations within and between the different groups. Comparisons between groups (EPE vs. UP, LPE vs. UP, GH vs. UP, and SGA vs. UP) were performed at corresponding UP gestational age. For both outcomes, it was investigated whether there was a linear, quadratic, or cubic evolution during the pregnancy and whether this evolution was different for the two groups. Model selection was done using backward elimination, i.e., non-significant terms were removed from the model in a stepwise manner. All analyses were performed using SAS^® version 9.4 (SAS Institute, Cary NC).