Fig. 1

The position of region of interest (ROI). The left panel indicates position of the eight different ROI sizes in gestational age group III in the left ventricular wall. Different colors indicate different ROI sizes (height × width). Yellow (2 × 2 mm), turquoise (3 × 3 mm), red (4 × 3 mm), green (4 × 4 mm), orange (6 × 3 mm), pink (6 × 4 mm), grey (8 × 3 mm) and blue (8 × 4 mm). The right panel shows the velocity traces produced. Sm = peak systolic myocardial velocity. Em = peak early diastolic myocardial velocity. Am = peak myocardial velocity during atrial contraction