Table 2.
Mean differences (95% confidence intervals) in standardised cognitive score for each birthweight category compared with middle birthweight category for tests at ages 8, 11, 15, and 26 years
| Birth weight (kg) | No (%) of participants | Adjusted* | Conditional on previous test score† | P value‡ |
|---|---|---|---|---|
| Age 8 years (n=3773): | ||||
| 0-2.50 | 174 (4.6) | −0.25 (−0.40 to −0.12) | — | <0.001 |
| 2.51-3.00 | 618 (16.4) | −0.06 (−0.15 to 0.02) | ||
| 3.01-3.50 | 1319 (35.0) | 0 | ||
| 3.51-4.00 | 1242 (32.9) | 0.16 (0.09 to 0.23) | ||
| 4.01-5.00 | 420 (11.1) | 0.18 (0.08 to 0.28) | ||
| Age 11 years (n=3527): | ||||
| 0-2.50 | 155 (4.4) | −0.21 (−0.36 to −0.07) | −0.02 (−0.12 to 0.07) | 0.51 |
| 2.51-3.00 | 586 (16.6) | −0.09 (−0.17 to 0.00) | −0.04 (−0.09 to 0.02) | |
| 3.01-3.50 | 1233 (35.0) | 0 | 0 | |
| 3.51-4.00 | 1159 (32.9) | 0.11 (0.04 to 0.18) | −0.01 (−0.05 to 0.04) | |
| 4.01-5.00 | 394 (11.2) | 0.08 (−0.02 to 0.18) | −0.04 (−0.11 to 0.02) | |
| Age 15 years (n=3383): | ||||
| 0-2.50 | 151 (4.5) | −0.24 (−0.39 to −0.10) | −0.06 (−0.14 to 0.02) | 0.14 |
| 2.51-3.00 | 564 (16.7) | −0.12 (−0.20 to −0.03) | −0.04 (−0.09 to 0.00) | |
| 3.01-3.50 | 1174 (34.7) | 0 | 0 | |
| 3.51-4.00 | 1117 (33.0) | 0.06 (−0.01 to 0.13) | −0.03 (−0.07 to 0.00) | |
| 4.01-5.00 | 377 (11.1) | 0.08 (−0.02 to 0.18) | 0.00 (−0.05 to 0.05) | |
| Age 26 years (n=2888): | ||||
| 0-2.50 | 135 (4.7) | −0.24 (−0.40 to −0.08) | −0.01 (−0.12 to 0.09) | 0.96 |
| 2.51-3.00 | 471 (16.3) | −0.09 (−0.18 to 0.01) | 0.01 (−0.06 to 0.07) | |
| 3.01-3.50 | 1006 (34.8) | 0 | 0 | |
| 3.51-4.00 | 966 (33.5) | 0.06 (−0.02, 0.14) | 0.02 (−0.04, 0.07) | |
| 4.01-5.00 | 310 (10.7) | 0.09 (−0.03 to 0.20) | 0.02 (−0.05 to 0.10) |
*
For sex, father's social class, mother's education, birth order, and mother's age.
†
Adjusted for all factors listed above, as well as for cognitive score at the previous age.
‡
P value for test for heterogeneity across birthweight groups for conditional analysis.