Table 1. Baseline Characteristics of the Participants by the Intervention Groupa.
| Characteristic | 400-IU group (n = 404), No. (%) | No. | 1200-IU group (n = 397), No. (%) | No. |
|---|---|---|---|---|
| Child | ||||
| At birth | ||||
| Female sex | 207 (51.2) | 404 | 198 (49.9) | 397 |
| Length of gestation, mean (SD), d | 280.7 (7.7) | 404 | 281.5 (7.5) | 397 |
| Season of birth | 404 | 397 | ||
| Winter | 83 (20.5) | 72 (18.1) | ||
| Spring | 166 (41.1) | 167 (42.1) | ||
| Summer | 85 (21.0) | 90 (22.7) | ||
| Autumn | 70 (17.3) | 68 (17.1) | ||
| 25(OH)D concentration at birth | ||||
| Cord blood, mean (SD) [range], ng/mL | 33.3 (11.4) [14.7-113.5] | 395 | 32.8 (9.5) [15.1-91.6] | 388 |
| ≤20 ng/mL | 9 (2.3) | 395 | 19 (4.9) | 388 |
| Mother | ||||
| Age at delivery, mean (SD), y | 31.0 (4.1) | 398 | 31.5 (4.6) | 397 |
| Smoking at childbirth, yes | 54 (13.7) | 395 | 57 (14.6) | 391 |
| Depressive symptoms at childbirth, mean (SD), scoreb | 12.1 (6.5) | 350 | 12.0 (6.1) | 352 |
| Educational level, highc | 292 (75.6) | 386 | 304 (77.6) | 392 |
Abbreviation: 25(OH)D, serum 25-hydroxyvitamin D.
SI conversion factor: To convert 25(OH)D to nanomoles per liter, multiply by 2.496.
a
Sample with data available on developmental milestones or social-emotional problems and competencies.
b
Depressive symptoms were measured with the Center for Epidemiological Studies Depression Scale.
c
Missing values were dummy-coded to their own category.