Table 1.
Sample characteristics*
| n † | Iron-fortified 244 |
Low-iron 229 |
|
|---|---|---|---|
| Infancy | |||
| Child characteristics | |||
| Male (n, %) | 125 (51.2) | 127 (55.5) | |
| Gestational age (wk) | 39.4 (0.07) | 39.5 (0.06) | |
| Birth weight (g) | 3511.3 (22.4) | 3524.7 (23.7) | |
| Weight-for-age z-score | 6 mo | 0.36 (0.06) | 0.38 (0.05) |
| 12 mo | −0.09 (0.06) | −0.15 (0.06) | |
| Height-for-age z-score | 6 mo | 0.10 (0.05) | 0.09 (0.05) |
| 12 mo | −0.14 (0.06) | −0.16 (0.05) | |
| Head circumference (cm) 6 mo | 43.8 (0.8) | 43.6 (0.7) | |
| 12 mo | 46.9 (0.9) | 46.7 (0.8) | |
| Hemoglobin (g/l) | 6 mo‡ | 111.9 (0.6) | 112.7 (0.6) |
| 12 mo | 124.3 (0.6) | 123.1 (0.6) | |
| Mean cell volume (fl) § | 12 mo | 74.7 (0.2) | 73.2 (0.3) |
| Ferritin (µg/l) § | 12 mo | 14.1 (0.6) | 10.3 (0.6) |
| Free erythrocyte protoporphyrin § 12 mo | |||
| (µmol/mol heme) | 83.5 (1.5) | 94.7 (2.2) | |
| [µg/dl red blood cells] | 94.3 (1.7) | 107.0 (2.5) | |
| Age at first bottle (mo) | 2.2 (0.1) | 2.2 (0.1) | |
| Still breastfed at 12 mo (n, %) | 45 (18.4) | 52 (22.7) | |
| Age at weaning if weaned (mo) | 4.6 (0.2) | 4.6 (0.2) | |
| Formula intake (ml/d) § | 609.9 (12.1) | 664.5 (12.3) | |
| 12-mo Bayley mental test scores | 105.2 (0.8) | 103.7 (0.8) | |
| 12-mo Bayley motor test scores | 97.9 (0.9) | 97.5 (1.0) | |
| Family characteristics | |||
| Maternal education (y) | 9.4 (0.2) | 9.2 (0.2) | |
| Paternal education (y) | 8.6 (0.2) | 8.4 (0.2) | |
| Father present (n, %) | 201 (83.1) | 184 (81.8) | |
| Number of children for mother | 2.2 (0.1) | 2.1 (0.1) | |
| Maternal IQ‖ | 84.4 (0.7) | 84.0 (0.7) | |
| Maternal depression¶ | 16.8 (0.8) | 16.3 (0.8) | |
| Maternal smoking in infancy (n, %) | 47, 20.9 | 42, 17.4 | |
| Social class index** | 27.3 (0.4) | 28.1 (0.5) | |
| Life stress†† | 4.5 (0.2) | 4.7 (0.2) | |
| Home environment‡‡ | 30.5 (0.3) | 30.7 (0.3) | |
| 10-year | |||
| Child characteristics | |||
| Age at testing (y) | 10.0 (0.0) | 10.0 (0.0) | |
| Male (n, %) | 129 (50.2) | 130 (53.7) | |
| Weight-for-age z-score | 0.42 (0.06) | 0.37 (0.06) | |
| Height-for-age z-score | −0.06 (0.06) | −0.12 (0.06) | |
| Body mass index | 19.3 (0.2) | 18.9 (0.2) | |
| Head circumference (cm) | 54.3 (0.1) | 54.2 (0.1) | |
| Hemoglobin (g/l) | 136.7 (0.5) | 137.7 (0.5) | |
| Mean cell volume (fl) | 82.0 (0.2) | 82.3 (0.2) | |
| Transferrin saturation (%) | 27.3 (9.0) | 25.9 (9.1) | |
| Ferritin (µg/l) | 30.1 (0.9) | 29.1 (0.9) | |
| Free erythrocyte protoporphyrin | |||
| (µmol/mol heme) | 50.0 (1.2) | 49.7 (1.0) | |
| [µg/dl red blood cells] | 56.5 (1.4) | 56.2 (1.1) | |
| Family characteristics | |||
| Maternal education (y) | 9.8 (0.2) | 9.5 (0.2) | |
| Paternal education (y) | 9.8 (0.2) | 9.8 (0.2) | |
| Father present (n, %) | 182 (71.4) | 170 (70.2) | |
| Maternal depression¶ | 18.6 (0.9) | 19.8 (0.9) | |
| Social class index** | 23.8 (0.4) | 24.7 (0.4) | |
| Life stress†† | 5.1 (0.2) | 5.1 (0.2) | |
| Home environment‡‡ | 36.8 (0.5) | 36.9 (0.5) | |
Values are means (SE) for continuous variables and percentages and n (%) for categorical variables.
ns vary slightly due to occasional missing data for some measures.
HemaCue at 6 mo.
The only statistically significant group differences were iron status measures in infancy by design and mean daily formula intake in infancy (low-iron group consumed about 54 ml more per day, t1,471 = 3.16, p = .002).
Measured by a short form of the Wechsler Adult Intelligence Scale-Revised.31
Measured by Center for Epidemiologic Studies Depression Scale.32
Measured by the Graffar scale, designed to differentiate families at the lower end of the socioeconomic spectrum;33 higher values indicate lower social class.
Measured by a scale modified from the Social Readjustment Rating Scale34
Measured by the Home Observation for Measurement of the Environment-Revised.35