Unadjusted associations of early life characteristics with intelligence at age 7 years among 11679 participants with intelligence scores
| N* | Mean (SD) | Mean difference (95% CI) | p Value† | ||
|---|---|---|---|---|---|
| *Numbers differ because of missing data for some predictor variables—these results are only on those with complete data for each predictor with no imputed data. †For most ordered categorical variables, and for birth weight and childhood anthropometric measures, p values are for tests of linear trends. For binary exposures they are t tests for differences between the two categories, and for method of delivery and gestational age, they are F tests for differences between categories. Results are not adjusted for sex or any other covariates. | |||||
| Parental characteristics | |||||
| Social class at birth | I and II | 1031 | 119.2 (14.7) | ref | <0.001 |
| III NM | 1301 | 112.9 (15.6) | −6.32 (−7.59, −5.05) | ||
| III M | 5185 | 107.5 (16.0) | −11.75 (−12.79, −10.71) | ||
| IV | 1643 | 102.8 (14.8) | −16.43 (−17.64, −15.22) | ||
| V (lowest) | 1920 | 100.4 (15.2) | −18.81 (−19.98, −17.63) | ||
| Gravidity | 1 | 3812 | 109.4 (16.2) | ref | <0.001 |
| 2 | 3374 | 108.5 (16.3) | −0.87 (−1.62, −0.13) | ||
| 3 | 2126 | 106.2 (16.3) | −3.14 (−4.00, −2.29) | ||
| 4 | 1169 | 103.9 (16.2) | −5.50 (−6.56, −4.45) | ||
| ⩾5 | 1198 | 100.1 (15.2) | −9.32 (−10.37, −8.27) | ||
| Birth outside marriage | No | 11181 | 107.3 (16.4) | ref | <0.001 |
| Yes | 498 | 100.9 (15.5) | −6.39 (−7.86, −4.93) | ||
| Maternal age at birth (years) | 15–19 | 530 | 102.1 (15.4) | ref | <0.001 |
| 20–24 | 3656 | 105.4 (15.8) | 3.22 (1.74, 4.71) | ||
| 25–29 | 3639 | 108.0 (16.5) | 5.84 (4.35, 7.33) | ||
| 30–34 | 2467 | 108.5 (16.7) | 6.40 (4.86, 7.93) | ||
| 35–39 | 1050 | 108.8 (16.7) | 6.65 (4.95, 8.36) | ||
| ⩾40 | 337 | 107.3 (16.7) | 5.17 (2.94, 7.40) | ||
| Maternal height (inches) | ⩽60 | 2993 | 104.1 (16.3) | ref | <0.001 |
| 61 | 1855 | 106.1 (16.2) | 2.02 (1.08, 2.96) | ||
| 62 | 2080 | 107.5 (16.1) | 3.48 (2.57, 4.39) | ||
| 63 | 1702 | 108.0 (16.7) | 3.93 (2.97, 4.90) | ||
| 64 | 1433 | 109.1 (15.9) | 5.00 (3.97, 6.02) | ||
| ⩾65 | 1616 | 110.4 (16.4) | 6.30 (5.31, 7.28) | ||
| Maternal physical condition | Very good or good | 4773 | 109.8 (16.0) | ref | <0.001 |
| Mediocre | 3228 | 105.3 (16.1) | −4.47 (−5.18, −3.76) | ||
| Very bad or bad | 797 | 99.9 (15.2) | −9.84 (−11.04, −8.65) | ||
| Pregnancy characteristics | |||||
| Pregnancy induced hypertension | No | 9702 | 106.7 (16.4) | ref | <0.001 |
| Yes | 1977 | 109.0 (16.4) | 2.35 (1.56, 3.14) | ||
| Antepartum haemorrhage | No | 11416 | 107.1 (16.4) | ref | 0.003 |
| Yes | 263 | 104.1 (17.9) | −3.00 (−5.01, −0.99) | ||
| Artificial rupture membranes | No | 9782 | 106.8 (16.4) | ref | 0.002 |
| Yes | 1897 | 108.2 (16.6) | 1.30 (0.50, 2.11) | ||
| Method of delivery | Normal vaginal | 10320 | 106.8 (16.4) | ref | <0.001 |
| Forceps | 761 | 110.4 (16.4) | 3.63 (2.42, 4.83) | ||
| Caesarean section | 340 | 111.8 (15.1) | 5.01 (3.25, 6.78) | ||
| Other assisted delivery | 257 | 102.9 (16.7) | −3.88 (−5.91, −1.86) | ||
| Birth characteristics | |||||
| Gestational age (weeks) | < 37 | 737 | 103.0 (16.7) | −5.17 (−6.41, −3.96) | <0.001 |
| 37–40 | 7521 | 108.2 (16.1) | ref | ||
| > 40 | 1095 | 107.4 (16.4) | −0.75 (−1.51, 0.02) | ||
| Birth weight (kg) | Per kg | 11658 | 4.21 (3.64, 4.79) | <0.001 | |
| Birth weight z score | Per SD | 10469 | 1.62 (1.31, 1.94) | <0.001 | |
| Childhood characteristics | |||||
| Height z score | Per SD | 11389 | 3.36 (3.06, 3.65) | < 0.001 | |
| Weight z score | Per SD | 11389 | 1.75 (1.45, 2.04) | < 0.001 | |
| BMI z score | Per SD | 11389 | −0.11 (−0.41, 0.19) | 0.47 | |
| Number of siblings at time of 1962 survey | 0 | 1078 | 111.5 (17.0) | ref | <0.001 |
| 1 | 3525 | 111.2 (15.7) | −0.27 (−1.35, 0.80) | ||
| 2 | 2952 | 108.0 (15.9) | −3.56 (−4.66, −2.46) | ||
| 3 | 2001 | 104.3 (15.7) | −7.25 (−8.43, −6.09) | ||
| ⩾4 | 2107 | 99.2 (15.2) | −12.28 (−13.44, −11.12) | ||