All births in England linked to delivery HES records by gestational age, 2005–2014.
| Gestational age | Number of ONS birth records | Linked to HES delivery record | Never linked to HES delivery record | Linkage rate |
| Missing or less than 22 weeks | 53 236 | 50 420 | 2816 | 94.71 |
| Preterm | 506 206 | 486 517 | 19 689 | 96.11 |
| Term | 5861 275 | 5678 501 | 182 774 | 96.88 |
| Post-term | 256 195 | 249 344 | 6851 | 97.33 |
| Total | 6676 912 | 6464 782 | 212 130 | 96.82 |
1884.065581 Pearson χ 2 statistic.
3 <- df = (rows− 1)× (columns− 1).
0.0000 <- getting the P value from the χ2 statistics and the df.
HES, Hospital Episode Statistics; ONS, Office for National Statistics.