Mother's mean age (years) | 32.2 | 32.0 | 0.820 |
Upper social classes 1–2 | 45 (64) | 62 (83) | 0.012 |
Lower social classes 3–4 | 25 (36) | 13 (17) | 0.012 |
Mother's smoking | 12 (17) | 9 (12) | 0.379 |
Primiparity | 41 (58) | 26 (35) | 0.004 |
Average number of children in family | 0.67 | 0.88 | 0.164 |
Response rate of mothers | 56 (80) | 66 (88) | 0.137 |
Response rate of fathers | 23 (33) | 38 (51) | 0.039 |
Birth weight (g) | 780 (447–995) | 3671 (2530–5250) | <0.001 |
Gestational age (weeks) | 27.1 (23.7–32.6) | 39.9 (37.3–42.1) | <0.001 |
Assessment age (years) | 2.24 (2.12–2.56) | 2.22 (1.91–2.73) | 0.524 |
Male | 37 (50) | 39 (52) | 0.807 |
SGA | 35 (47) | 1 (1) | <0.001 |
Multiple pregnancy infants | 16 (22) | 2 (3) | <0.001 |
Bayley scores <70 | 1 (1) | 0 | 0.497 |
Blindness at the age of 2 years | 0 | 0 | |
Cerebral palsy at the age of 2 years | 3 (4) | 0 | 0.245 |