Table 1.
Characteristics of 792 724 children in the sibling cohort
| Characteristics | Sibling cohort* (%) | % of children† | ||
|---|---|---|---|---|
| Born <37 weeks | Language: z score <0 | Math: z score <0 | ||
| Gestational age at birth (weeks) | ||||
| ≤27 | 930 (0.1) | 100 | 60.9 | 67.1 |
| 28-31 | 4686 (0.6) | 100 | 54.5 | 59.6 |
| 32-33 | 6234 (0.8) | 100 | 53.2 | 53.8 |
| 34-36 | 32 472 (4.1) | 100 | 50.6 | 51.1 |
| 37 | 36 932 (4.7) | 0 | 49.6 | 51.1 |
| 38 | 87 494 (11.0) | 0 | 48.7 | 50.2 |
| 39 | 162 285 (20.5) | 0 | 47.0 | 48.3 |
| 40 | 240 045 (30.3) | 0 | 45.7 | 47.2 |
| 41 | 142 808 (18.0) | 0 | 45.0 | 46.5 |
| ≥42 | 65 891 (8.3) | 0 | 46.6 | 47.4 |
| Missing | 12 947 (1.6) | - | 47.3 | 50.2 |
| Sex | ||||
| Female | 384 787 (48.5) | 5.2 | 35.4 | 49.1 |
| Male | 407 937 (51.5) | 5.9 | 57.5 | 47.3 |
| Relative birth weight by gestational week (centile) | ||||
| 0-4 | 34 649 (4.4) | 5.6 | 51.8 | 58.7 |
| 5-9 | 34 583 (4.4) | 5.8 | 48.9 | 55.6 |
| 10-24 | 108 607 (13.7) | 5.6 | 47.4 | 52.1 |
| 25-49 | 190 904 (24.1) | 5.4 | 46.2 | 48.9 |
| 50-74 | 197 164 (24.9) | 5.2 | 45.4 | 46.0 |
| 75-89 | 123 601 (15.6) | 5.3 | 46.0 | 44.3 |
| 90-95 | 42 833 (5.4) | 4.7 | 47.2 | 43.4 |
| 95-100 | 43 238 (5.5) | 4.8 | 48.1 | 43.7 |
| Missing | 17 145 (2.2) | 19.2 | 51.0 | 54.4 |
| Malformations | ||||
| Present | 91 504 (11.5) | 8.6 | 51.0 | 52.9 |
| Not present | 701 220 (88.5) | 5.2 | 46.2 | 47.5 |
| Maternal age at childbirth (years) | ||||
| <20 | 12 388 (1.6) | 6.7 | 71.3 | 76.2 |
| 20-24 | 134 507 (17.0) | 5.6 | 57.9 | 60.4 |
| 25-29 | 321 076 (40.5) | 5.2 | 46.1 | 47.0 |
| 30-34 | 241 714 (30.5) | 5.6 | 41.9 | 43.1 |
| 35-39 | 74 407 (9.4) | 6.8 | 41.6 | 43.1 |
| ≥40 | 8632 (1.1) | 8.0 | 43.7 | 45.3 |
| Maternal educational level‡ | ||||
| Primary education | 200 368 (25.3) | 6.5 | 64.0 | 69.0 |
| Upper secondary education | 80 948 (10.2) | 4.9 | 38.9 | 39.9 |
| Vocational education and training | 276 575 (34.9) | 5.7 | 48.2 | 49.4 |
| Short term higher education | 29 223 (3.7) | 5.3 | 39.1 | 35.7 |
| Vocational bachelor education | 147 410 (18.6) | 4.8 | 32.6 | 32.2 |
| Academic bachelor’s degree | 8287 (1.0) | 5.0 | 28.2 | 26.1 |
| Academic master’s degree | 40 577 (5.1) | 4.6 | 24.5 | 20.1 |
| PhD or other doctoral degree | 1284 (0.2) | 4.8 | 22.5 | 15.3 |
| No maternal education stated | 8052 (1.0) | 6.7 | 71.9 | 75.8 |
| No of older full siblings | ||||
| 0 | 331 978 (41.9) | 7.2 | 43.5 | 44.3 |
| 1 | 336 071 (42.4) | 4.4 | 47.8 | 49.5 |
| 2 | 96 471 (12.2) | 4.3 | 50.3 | 52.3 |
| 3 | 20 639 (2.6) | 5.2 | 57.4 | 60.5 |
| ≥4 | 7565 (1.0) | 5.9 | 67.0 | 71.3 |
| Diagnosis of prematurity morbidity§ (among children born <37 weeks) | ||||
| Yes | 1762 (4.0) | 100 | 62.5 | 67.7 |
| No | 42 560 (96.0) | 100 | 51.1 | 52.1 |
See supplementary table S1 for additional characteristics of the cohort.
Created from a population cohort of 1 161 406 children, of whom 9286 died before age 16 years. Among those who died, 35.1% were born before 37+0 gestational weeks.
Among those with a registered gestational age and grades for written language and mathematics examinations, respectively.
Highest educational level attained at time of childbirth. See supplementary table S3 for description and examples of specific educational categories.
Diagnosis of neurological birth trauma, retinopathy of prematurity, respiratory impairment owing to prematurity, cardiovascular impairment owing to prematurity, neonatal non-traumatic haemorrhage or haemolytic disease, gastrointestinal impairment owing to prematurity, or other registered neonatal cerebral damage (see supplementary table S2 for diagnostic codes).