Table. Characteristics of the Total Study Population (N = 47 045).
| No. of Participants/ Total No. (%)a |
Median (95% Range) | |
|---|---|---|
| Maternal Demographics | ||
| Age, y | 46 893 | 29.0 (5.2)b |
| Gestational age at blood sampling, wk | 46 876 | 12.9 (7.0-39.7) |
| Body mass indexc | 31 728 | 23.9 (4.4)b |
| Parity | ||
| 0 | 24 180/44 336 (54.5) | |
| 1 | 13 217/44 336 (29.8) | |
| 2 | 4435/44 336 (10.0) | |
| ≥3 | 2504/44 336 (5.6) | |
| Smoking status | ||
| Nonsmoker or past smoker | 38 733/43 662 (88.7) | |
| Current smoker | 4929/43 662 (11.3) | |
| Education leveld | ||
| Low | 9677/31 574 (30.6) | |
| Middle | 10 647/31 574 (33.7) | |
| High | 11 250/31 574 (35.6) | |
| Maternal Concentrations | ||
| Thyrotropin, mIU/Le | 46 421 | 1.33 (0.13-4.52) |
| Free thyroxine, pmol/L | 46 291 | 13.0 (7.2-21.9) |
| Thyroid peroxidase antibody positivity | 3043/40 559 (7.5) | |
| Thyroglobulin antibody positivity | 1080/18 548 (5.8) | |
| Pregnancy Characteristics | ||
| Gestational age at birth, wk | 47 045 | 39.9 (35.3-42.0) |
| Sex | ||
| Male | 18 936/37 355 (50.7) | |
| Female | 18 419/37 355 (49.3) | |
| Late preterm birth (gestational age <37 wk)f | 2357/47 045 (5.0) | |
| Early preterm birth (gestational age <32 wk) | 349/47 045 (0.7) | |
SI conversion factor: To convert free thyroxine to ng/dL, divide by 12.871.
a
The total No. indicates the No. of participants with available data on the thyroid function tests. Cohort-specific descriptive characteristics appear in eTable 1 in Supplement 2.
b
Expressed as mean (SD).
c
Calculated as weight in kilograms divided by height in meters squared.
d
Defined as estimated years of education beyond primary school (low: 0-4 years; middle: 4-8 years; high: >8 years).
e
Often referred to as thyroid-stimulating hormone or TSH.
f
Includes very preterm birth (<32 weeks’ gestational age).