All births in England linked to delivery HES records by age of mother, 2005–2014.
| Age of mother | Number of ONS birth records | Linked to HES delivery record | Never linked to HES delivery record | Linkage rate |
| Under 15 | 1739 | 1653 | 86 | 95.05 |
| 15–19 | 206 936 | 200 367 | 6569 | 96.83 |
| 20–24 | 1218 562 | 1186 178 | 32 384 | 97.34 |
| 25–29 | 1812 830 | 1764 402 | 48 428 | 97.33 |
| 30–34 | 1926 290 | 1865 427 | 60 863 | 96.84 |
| 35–39 | 1092 622 | 1048 332 | 44 290 | 95.95 |
| 40–44 | 245 526 | 232 397 | 13 129 | 94.65 |
| 45 and more | 15 821 | 14 020 | 1801 | 88.62 |
| Not stated | 156 586 | 152 006 | 4580 | 97.08 |
| Total | 6676 912 | 6464 782 | 212 130 | 96.82 |
12579.68484 Pearson χ2 statistic.
8 <- 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.