Table 1.
Selected characteristics of the study population for the total sample and stratified by infant sex.
| Characteristicsa,b | Total sample (n = 989) | Female (n = 492) | Male (n = 497) |
|---|---|---|---|
| Male/female infants | 497 (50%)/492 (50%) | 492 (100%) | 497 (100%) |
| Head circumference (cm) | 35.00 (28.00, 34.00–35.50, 41.43) | 34.50 (30.25, 33.50–35.00, 41.43) | 35.00 (28.00, 34.00–36.00, 40.00) |
| Length (cm) | 50.80 (40.1, 49.00–52.70, 62.23) | 50.80 (43.00, 48.30–52.07, 60.96) | 51.00 (40.01, 49.53–53.30, 62.23) |
| Weight (g) | 3,459 (1,380, 3,160–3,742, 5,400) | 3,382 (2,040, 3,105–3,706, 4,710) | 3,537 (1,380, 3,230–3,814, 5,400) |
| Gestational age at delivery (weeks) | 39.1 (30.9, 38.4–40.0, 44.7) | 39.1 (33.0, 38.4–40.0, 44.7) | 39.1 (30.9, 38.4–40.0, 43.0) |
| Age at enrollment (years) | 31.4 (19.3, 28.4–34.6, 44.8) | 31.6 (19.5, 28.9–31.7, 44.5) | 31.3 (19.3, 28.2–34.7, 44.8) |
| Maternal BMI | 24.27 (16.88, 21.80–28.29, 48.18) | 24.33 (17.07, 21.63–28.16, 45.72) | 24.13 (16.88, 21.97–28.34, 48.18) |
| Smoke during pregnancy | 54 (5%) | 29 (6%) | 25 (5%) |
| Maternal highest attained level of education: | |||
| Less than 11th grade or high school graduate or equivalent | 97 (10%) | 53 (11%) | 44 (9%) |
| Junior college graduate or some college or technical school | 180 (18%) | 91 (18%) | 89 (18%) |
| College graduate | 405 (41%) | 195 (40%) | 210 (42%) |
| Any post-graduate schooling | 307 (31%) | 153 (31%) | 154 (31%) |
| Postnatal toenails (μg/g) | |||
| As | 0.05 (0.01, 0.04–0.09, 0.74) | 0.05 (0.01, 0.04–0.09, 0.74) | 0.05 (0.01, 0.03–0.09, 0.70) |
| Mn | 0.32 (0.03, 0.18–0.62, 19.95) | 0.33 (0.03, 0.18–0.69, 19.95) | 0.30 (0.04, 0.18–0.58, 16.12) |
| Pb | 0.11 (0.00, 0.06–0.22, 23.12) | 0.11 (0.01, 0.06–0.22, 23.12) | 0.11 (0.00, 0.06–0.22, 6.11) |
Categorical variables = n (%).
Continuous variable = median (min., IQR, max.)