Fig. 5

Meta-regression curve of spiral artery measurements (Resistance Index) during first, second and third trimester in healthy pregnancies. Every color is representing one article, except for Matijevic et al. (ref. [9]) and Hsieh et al. (ref. [23]) who have two colors representing central and peripheral located spiral artery measurements. ‘N’ represents the maximum amount of cases included in the study, shown as a small or larger circle