| Gestational age (weeks+days) based on the first day of LMP | Change LMP-based EDD to ultrasound-based EDD if ultrasound-based gestational age differs from LMP-based gestational age by more than: |
| ≤8+6 | 5 days |
| 9+0 to 13+6 | 7 days |
| 14+0 to 15+6 | 7 days |
| 16+0 to 21+6 | 10 days |
| 22+0 to 27+6 | 14 days |
| ≥28+0 | 21 days |
