Frequencies of HG appearance in the three orthogonal planes according to GA groups
| GA (week) | Sagittal Plane (%) | Coronal Plane (%) | Axial Plane (%) |
|---|---|---|---|
| 19–21 | 0 | 0 | 0 |
| 22–23 | 0 | 0 | 0 |
| 24–25 | 67 | 9.5 | 0 |
| 26–27 | 94 | 88.8 | 67 |
| 28–29 | 100 | 100 | 100 |
| 30–31 | 100 | 100 | 100 |
| 32–33 | 100 | 100 | 100 |
| 34–39 | 100 | 100 | 100 |