| Characteristic | Before MI | After MI (%) | IQ | ||
| No | % | Mean (SD) | 95% CI | ||
| Environmental and personal factors | |||||
| Maternal age at birth (years) | |||||
| <25 | 174 | 31.6 | 34.9 | 94.9 (15.0) | 94.2 to 95.7 |
| 25–30 | 214 | 38.9 | 38.0 | 99.5 (16.0) | 99.1 to 99.9 |
| >30 | 162 | 29.5 | 27.1 | 99.2 (15.3) | 98.7 to 99.6 |
| Parental education | |||||
| Low | 172 | 32.0 | 38.9 | 92.2 (14.3) | 91.2 to 93.2 |
| Intermediate | 208 | 38.2 | 36.2 | 98.6 (15.0) | 98.2 to 99.0 |
| High | 162 | 29.8 | 24.9 | 106.2 (14.7) | 105.7 to 106.7 |
| Sex | |||||
| Male | 255 | 45.4 | 51.8 | 98.8 (16.6) | 98.5 to 99.2 |
| Female | 307 | 54.6 | 48.2 | 96.7 (14.4) | 96.4 to 97.1 |
| Origin | |||||
| Caucasian | 496 | 89.2 | 85.3 | 98.1 (15.6) | 97.8 to 98.3 |
| Non-Caucasian | 60 | 10.8 | 14.7 | 96.5 (15.2) | 95.8 to 97.1 |
| Neonatal factors | |||||
| Gestational age (weeks) | |||||
| <32 | 413 | 73.6 | 70.5 | 98.4 (15.9) | 98.1 to 98.7 |
| ⩾32 | 148 | 28.4 | 29.5 | 96.4 (14.9) | 96.0 to 96.9 |
| Growth | |||||
| AGA | 274 | 56.5 | 53.7 | 99.7 (15.7) | 98.7 to 100.7 |
| AGA-NGR | 79 | 16.3 | 17.3 | 95.5 (15.8) | 93.6 to 97.4 |
| Asymmetric IUGR | 46 | 9.5 | 12.1 | 97.4 (14.6) | 96.7 to 98.1 |
| Symmetric IUGR | 86 | 17.2 | 16.9 | 94.6 (14.9) | 94.0 to 95.2 |
AGA, appropriate size for gestational age; IUGR, intrauterine growth retardation; AGA-NGR, neonatal growth restraint.