Cognitive test scores in extremely preterm (EP) participants and term-born controls by age of assessment, overall and stratified by sex, maternal education, neonatal brain injury and gestational age
| Age 2.5 years | Age 6 years | Age 11 years | Age 19 years | ||||
| EP (n=283) | EP (n=241) | Control (n=160) | EP (n=219) | Control (n=153) | EP (n=127) | Control (n=64) | |
| Cognitive test* | BSID-II MDI | K-ABC MPC | K-ABC MPC | WASI-II FSIQ | |||
| Age at assessment† | |||||||
| Mean (SD) | 2.5 (0.1) | 6.3 (0.5) | 6.1 (0.5) | 11.0 (0.4) | 11.0 (0.6) | 19.3 (0.6) | 19.2 (0.5) |
| Median (range) | 2.5 (2.3–3.3) | 6.3 (5.2–7.3) | 6.2 (5.1–7.2) | 10.9 (10.2–12.2) | 10.9 (9.8–12.3) | 19.3 (18.4–20.5) | 19.2 (18.1–20.1) |
| Cognitive test score‡ | |||||||
| Mean (95% CI) | 78.7 (76.7 to 80.7) | 81.6 (79.0 to 84.2) | 105.7 (103.9 to 107.6) | 83.4 (80.8 to 85.9) | 104.1 (102.3 to 105.8) | 85.7 (82.7 to 88.8) | 103.9 (101.4 to 106.4) |
| Mean difference (95% CI) | −24.2 (−27.7 to −20.6) | −20.7 (−24.1 to −17.3) | −18.1 (−22.8 to −13.5) | ||||
| Infant sex | |||||||
| Female | |||||||
| n (%) | 148 (52.3) | 119 (49.4) | 89 (55.6) | 118 (53.9) | 89 (58.2) | 68 (53.5) | 39 (60.9) |
| Mean (95% CI) | 82.4 (80.0 to 84.9) | 87.2 (83.9 to 90.4) | 105.5 (103.2 to 107.8) | 87.6 (84.5 to 90.6) | 104.2 (102.2 to 106.3) | 88.6 (84.9 to 92.3) | 103.6 (100.7 to 106.5) |
| Male | |||||||
| n (%) | 135 (47.7) | 122 (50.6) | 71 (44.4) | 101 (46.1) | 64 (41.8) | 59 (46.5) | 25 (39.1) |
| Mean (95% CI) | 74.6 (71.7 to 77.6) | 76.1 (72.3 to 79.9) | 106.0 (103.0 to 109.0) | 78.5 (74.4 to 82.6) | 103.8 (100.8 to 106.9) | 82.4 (77.6 to 87.2) | 104.4 (99.7 to 109.0) |
| Mean difference (95% CI) | −7.8 (−11.6 to −4.0) | −11.1 (−16.2 to −6.1) | 0.5 (−3.3 to 4.2) | −9.1 (−14.1 to −4.0) | −0.4 (−4.0 to 3.2) | −6.2 (−12.2 to −0.2) | 0.8 (−4.5 to 6.1) |
| Maternal education | |||||||
| O’ level or below | |||||||
| n (%) | 174 (61.5) | 146 (60.6) | 82 (51.3) | 131 (59.8) | 87 (56.9) | 64 (50.4) | 32 (50.0) |
| Mean (95% CI) | 77.9 (75.4 to 80.4) | 80.6 (77.4 to 83.8) | 104.7 (102.1 to 107.2) | 82.7 (79.4 to 86.1) | 102.6 (100.3 to 104.8) | 85.6 (81.7 to 89.4) | 103.4 (99.4 to 107.3) |
| A’ level or above | |||||||
| n (%) | 95 (33.6) | 83 (34.4) | 59 (36.9) | 77 (35.2) | 58 (37.9) | 60 (47.2) | 31 (48.4) |
| Mean (95% CI) | 81.1 (77.9 to 84.3) | 83.8 (79.0 to 88.7) | 108.7 (105.6 to 111.7) | 86.3 (82.1 to 90.6) | 106.1 (103.0 to 109.1) | 87.3 (82.7 to 91.8) | 104.3 (101.1 to 107.5) |
| Mean difference (95% CI) | 3.2 (−1.0 to 7.4) | 3.2 (−2.4 to 8.9) | 4.0 (−0.01 to 8.0) | 3.6 (−1.8 to 9.0) | 3.5 (−0.2 to 7.2) | 1.7 (−4.3 to 7.7) | 0.9 (−4.3 to 6.2) |
| Neonatal brain injury | |||||||
| No/mild brain injury | |||||||
| n (%) | 220 (77.7) | 187 (77.6) | 160 (100) | 169 (77.2) | 153 (100) | 104 (81.9) | 164 (100) |
| Mean (95% CI) | 80.5 (78.3 to 82.6) | 85.2 (82.7 to 87.7) | – | 86.1 (83.6 to 88.5) | – | 87.2 (84.2 to 90.2) | – |
| Moderate/severe brain injury | |||||||
| n (%) | 63 (22.3) | 54 (22.4) | 0 (0.0) | 49 (22.4) | 0 (0.0) | 22 (17.3) | 0 (0.0) |
| Mean (95% CI) | 72.7 (68.1 to 77.3) | 68.9 (62.0 to 75.8) | – | 73.8 (66.5 to 81.0) | – | 78.4 (68.8 to 88.1) | – |
| Mean difference (95% CI) | −7.8 (−12.4 to −3.12) | −16.3 (−22.3 to 10.4) | – | −12.3 (−18.3 to −6.3) | – | −8.7 (−16.7 to −0.8) | – |
| Gestational age at delivery | |||||||
| 25 weeks | |||||||
| n (%) | 167 (59.0) | 144 (59.8) | 0 (0.0) | 126 (57.5) | 0 (0.0) | 75 (59.1) | 0 (0.0) |
| Mean (95% CI) | 79.8 (77.5 to 82.2) | 84.3 (81.2 to 87.5) | – | 86.1 (83.3 to 88.9) | – | 87.6 (84.2 to 91.0) | – |
| <25 weeks | |||||||
| n (%) | 116 (41.0) | 97 (40.2) | 0 (0.0) | 93 (42.5) | 0 (0.0) | 52 (40.9) | 0 (0.0) |
| Mean (95% CI) | 77.1 (73.8 to 80.4) | 77.4 (73.1 to 81.8) | – | 79.7 (75.1 to 84.4) | – | 83.1 (77.7 to 88.6) | – |
| Mean difference (95% CI) | −2.7 (−6.7 to 1.3) | −6.9 (−12.2 to 1.6) | – | −6.3 (−11.5 to 1.2) | – | −4.5 (−10.6 to 1.7) | – |
*BSID-II MDI, Bayley Scales of Infant Development -Second Edition Mental Development Index; K-ABC MPC, Kaufman Assessment Battery for Children mental processing composite; WASI-II FSIQ, Wechsler Abbreviated Scale of Intelligence-Second Edition – Full Scale IQ.
†Corrected age at year 2.5 and chronological age in years 6, 11 and 19.
‡Values were multiply imputed within a clinically specified range for EP participants seen at assessment but not tested with planned cognitive test: n=52 (year 2.5), n=41 (year 6), n=18 (year 11), n=3 (year 19). Values were multiply imputed for one control in year 6.