TABLE 1.
Population characteristics1
| Generation R (n = 1634) | INMA (n = 1293) | ALSPAC (n = 2619) | ||||
|---|---|---|---|---|---|---|
| n | Values | n | Values | n | Values | |
| ADHD,2 % | 1588 | 3.5 | 1066 | 5.0 | 2611 | 1.7 |
| Autistic traits ≥93rd percentile, % | 1291 | 7.4 | 1111 | 8.5 | 2585 | 8.0 |
| Iodine status, all women | ||||||
| UI/Creat, μg/g | 1634 | 212 (153–291) | 1293 | 168 (110–255) | 2619 | 131 (88–203) |
| UI/Creat <150 μg/g, % | 1634 | 23.4 | 1293 | 43.1 | 2619 | 58.7 |
| Gestational age, wk | 1634 | 16.1 (15.0–17.3) | 1293 | 20.6 (19.5–21.8) | 2619 | 13.0 (9.2–17.0) |
| Iodine status at ≤18 wk | ||||||
| UI/Creat, μg/g | 1555 | 211 (141–309) | 1161 | 154 (97–259) | 2403 | 125 (85–198) |
| UI/Creat <150 μg/g, % | 1555 | 28.0 | 1161 | 48.5 | 2403 | 61.0 |
| Gestational age, wk | 1555 | 12.9 (12.1–14.4) | 1161 | 12.9 (12.3–13.7) | 2403 | 12.0 (9.0–15.0) |
| Iodine status at ≤14 wk | ||||||
| UI/Creat, μg/g | 1082 | 210 (141–303) | 952 | 157 (99–265) | 1530 | 111 (75–165) |
| UI/Creat <150 μg/g, % | 1082 | 28.0 | 952 | 47.5 | 1530 | 69.7 |
| Gestational age, wk | 1082 | 12.4 (11.6–13.1) | 952 | 12.7 (12.1–13.3) | 1530 | 10.0 (8.0–12.0) |
| Maternal thyroid function | ||||||
| TSH, mIU/L | 1451 | 1.32 (0.81–2.01) | 1251 | 1.25 (0.84–1.80) | 965 | 0.98 (0.64–1.40) |
| FT4, pmol/L | 1459 | 14.5 (13.0–16.4) | 1253 | 10.6 (9.7–11.6) | 970 | 16.2 (14.9–17.6) |
| TPOAb positivity, % | 1470 | 5.4 | NA | 973 | 12.7 | |
| Gestational age, wk | 1460 | 13.2 ± 1.8 | 1252 | 13.2 ± 1.4 | 979 | 10.3 ± 2.7 |
| Female sex, % | 1634 | 50.1 | 1292 | 49.8 | 2619 | 50.7 |
| Educational level,3 % | 1580 | 1289 | 2570 | |||
| Low | 6.5 | 21.0 | 18.7 | |||
| Middle | 39.7 | 41.1 | 62.8 | |||
| High | 53.9 | 37.6 | 18.5 | |||
| Maternal ethnicity/country of birth, % | 1633 | 1291 | 2562 | |||
| Majority4 | 56.8 | 93.5 | 98.6 | |||
| Minority5 | 43.2 | 6.5 | 1.4 | |||
| Maternal age, y | 1634 | 30.8 ± 4.6 | 1281 | 31.6 ± 3.9 | 2619 | 28.7 ± 4.4 |
| Parity, % | 1634 | 1291 | 2545 | |||
| 0 | 60.0 | 56.2 | 47.6 | |||
| 1 | 28.7 | 37.1 | 34.0 | |||
| ≥2 | 11.3 | 6.6 | 18.5 | |||
| Smoking during pregnancy, % | 1490 | 1293 | 2586 | |||
| Never | 76.6 | 69.9 | 84.4 | |||
| In the beginning of pregnancy | 10.0 | 13.2 | 3.7 | |||
| Continued | 13.4 | 16.9 | 11.9 | |||
| Prepregnancy BMI, kg/m2 | 1450 | 22.6 (20.8–25.1) | 1293 | 22.5 (20.8–25.0) | 2417 | 22.2 (20.5–24.4) |
Values are means ± SDs, medians (IQRs), or percentages. Values are shown without multiple imputation (percentages of missing data: 0.0%, 0.1%, and 0.0% for child sex; 3.3%, 0.3%, and 1.9% for maternal education; 0.1%, 0.2%, and 2.1% for maternal ethnicity/country of birth; 0.1%, 0.9%, and 2.2% for maternal age; 0.0%, 0.2%, and 2.8% for parity; 8.8%, 1.3%, and 1.3% for smoking; and 11.3%, 0.0%, and 7.7% for prepregnancy BMI in Generation R, INMA, and ALSPAC, respectively). ADHD, attention-deficit hyperactivity disorder; ALSPAC, Avon Longitudinal Study of Parents and Children; FT4, free thyroxine; INMA, INfancia y Medio Ambiente; NA, not available; TPOAb, thyroid peroxidase antibody; TSH, thyroid-stimulating hormone; UI/Creat, urinary iodine-to-creatinine ratio.
ADHD diagnosis was established by interview but not confirmed by medical-record data.
Generation R: low = no education or primary; middle = secondary phase 1 and 2; high = higher phase 1 and 2; INMA: low = no education, unfinished primary, or primary; middle = secondary; high = university degree; ALSPAC: low = no qualification, certificate of secondary education, or vocational; middle = O level or A level; high = a degree.
Defined as Dutch (Generation R), Spanish (INMA), or white (ALSPAC).
Defined as non-Dutch (Generation R), non-Spanish (INMA), or nonwhite (ALSPAC).