Table. Descriptive Statistics of Study Participants.
| Exposures and Characteristics | Full Study Sample (n = 2050) | Full-term and Late-term (n = 1880) |
|---|---|---|
| Prenatal Air Pollutant Exposures | ||
| Particulate matter, μg/m3 | ||
| <2.5 μma | ||
| Mean (SD) | 21.5 (8.2) | 21.5 (8.2) |
| Median (IQR) | 24.2 (14.8-27.5) | 24.3 (14.8-27.5) |
| <10 μm | ||
| Mean (SD) | 42.0 (11.1) | 42.1 (11.0) |
| Median (IQR) | 41.8 (37.3-48.0) | 41.9 (37.4-48.0) |
| Nitrogen dioxide, ppb | ||
| Mean (SD) | 30.0 (10.8) | 30.0 (10.8) |
| Median (IQR) | 33.0 (22.8-37.4) | 33.0 (22.9-37.4) |
| Ozone, ppb | ||
| Mean (SD) | 44.9 (12.0) | 45.0 (11.9) |
| Median (IQR) | 44.3 (34.0-54.2) | 44.6 (34.1-54.3) |
| Nitrogen oxides, ppbb | ||
| Total | ||
| Mean (SD) | 27.2 (23.5) | 27.1 (23.0) |
| Median (IQR) | 21.1 (11.6-36.3) | 21.0 (11.7-36.1) |
| Freeway | ||
| Mean (SD) | 17.1 (20.3) | 16.9 (19.7) |
| Median (IQR) | 11.2 (4.2-22.6) | 11.1 (4.3-22.4) |
| Nonfreeway | ||
| Mean (SD) | 10.2 (7.3) | 10.2 (7.3) |
| Median (IQR) | 8.6 (5.2-13.8) | 8.6 (5.2-13.7) |
| Newborn and Pregnancy Characteristics | ||
| Age at blood spot collection, h | ||
| Mean (SD) | 27 (35) | 26 (35) |
| Median (IQR) | 20 (15-29) | 20 (15-28) |
| Time from blood spot collection until TT4 measurement, d | ||
| Mean (SD) | 3 (2) | 3 (2) |
| Median (IQR) | 3 (2-4) | 3 (2-4) |
| Heel stick TT4, μg/dL | ||
| Mean (SD) | 16.2 (4.3) | 16.4 (4.2) |
| Median (IQR) | 15.9 (13.3-18.8) | 16.0 (13.4-19.0) |
| Gestational age, d | ||
| Mean (SD) | 277 (15) | 280 (10) |
| Median (IQR) | 278 (270-285) | 279 (273-286) |
| Sex, No. (%) | ||
| Male | 1036 (50.5) | 950 (50.5) |
| Female | 1014 (49.5) | 930 (49.5) |
| Race/ethnicity, No. (%) | ||
| Hispanic white | 1202 (58.6) | 1089 (57.9) |
| Non-Hispanic white | 638 (31.1) | 599 (31.9) |
| Black | 66 (3.2) | 59 (3.1) |
| Other | 144 (7.0) | 133 (7.1) |
| Season of birth, No. (%) | ||
| Warm | 1151 (56.1) | 1050 (55.9) |
| Cool | 899 (43.9) | 830 (44.1) |
| Mode of delivery, No. (%) | ||
| Vaginal | 1628 (79.4) | 1491 (79.3) |
| Cesarean | 422 (20.6) | 389 (20.7) |
| Pregnancy complication, No. (%)c | ||
| Yes | 195 (9.5) | 163 (8.7) |
| No | 1855 (90.5) | 1717 (91.3) |
| Labor duration, No. (%) | ||
| Precipitous (<3 h) | 9 (0.4) | 9 (0.5) |
| Normal (3-20 h) | 2030 (99.0) | 1860 (98.9) |
| Prolonged (>20 h) | 11 (0.5) | 11 (0.6) |
| Principal payment source for prenatal care, No. (%) | ||
| None or government | 754 (36.8) | 671 (35.7) |
| Health insurance | 1233 (60.1) | 1153 (61.3) |
| Other | 63 (3.1) | 56 (3.0) |
| Maternal and Family Characteristics | ||
| Age, mean (SD), y | 27 (6) | 27 (6) |
| Education, No. (%) | ||
| Completed at least high school | 1486 (72.5) | 1382 (73.5) |
| Did not complete high school | 564 (27.5) | 498 (26.5) |
| Maternal smoking status during pregnancy, No. (%) | ||
| Ever | 145 (7.1) | 128 (6.8) |
| Never | 1905 (92.9) | 1752 (93.2) |
| Paternal smoking status during pregnancy, No. (%) | ||
| Ever | 307 (15.0) | 278 (14.8) |
| Never | 1685 (82.2) | 1548 (82.3) |
| Did not report | 58 (2.8) | 54 (2.9) |
| Parity, No. (%) | ||
| Parous | 1306 (63.7) | 1206 (64.1) |
| Nulliparous | 744 (36.3) | 674 (35.9) |
| Total household income, No. (%) | ||
| <$7500 | 91 (4.4) | 83 (4.4) |
| $7500-$14 999 | 157 (7.7) | 144 (7.7) |
| $15 000-$29 999 | 304 (14.8) | 271 (14.4) |
| $30 000-$49 999 | 359 (17.5) | 333 (17.7) |
| $50 000-$74 999 | 340 (16.6) | 319 (17.0) |
| $75 000-$99 999 | 268 (13.1) | 254 (13.5) |
| ≥$100 000 | 279 (13.6) | 261 (13.9) |
| Do not know or did not report | 252 (12.3) | 215 (11.4) |
Abbreviations: IQR, interquartile range; TT4, total thyroxine.
SI conversion factor: To convert TT4 to nanomoles per liter, multiply by 12.871.
a
Sample sizes were 2046 for full sample and 1876 for full- and late-term subset.
b
Sample sizes were 1989 for full sample and 1824 for full- and late-term subset.
c
Preeclampsia or pregnancy-induced hypertension, eclampsia, chronic hypertension, renal disease, pyelonephritis, anemia, cardiac disease, acute or chronic lung disease, diabetes, Rh sensitization, hemoglobinopathy, uterine bleeding before labor, polyhydramnios or oligohydramnios, incompetent cervix, premature labor, genital herpes, other sexually transmitted diseases, hepatitis B, or rubella.