Table 1. Characteristics of the Study Population by Daily MF Exposure Level Among Pregnant Women Participants.
| Characteristic | Total No.a | MF at 90th percentile, No. (%) | P valued | |
|---|---|---|---|---|
| Low (n = 572)b | High (n = 882)c | |||
| Maternal age, y | ||||
| ≤25 | 201 | 75 (13.1) | 126 (14.3) | .005 |
| 26-30 | 420 | 145 (25.4) | 275 (31.2) | |
| 31-35 | 472 | 183 (32.0) | 289 (32.8) | |
| ≥36 | 361 | 169 (29.6) | 192 (21.8) | |
| Race/ethnicity | ||||
| White | 548 | 213 (37.2) | 335 (38.0) | .79 |
| African American | 110 | 48 (8.4) | 62 (7.0) | |
| Hispanic | 325 | 125 (21.9) | 200 (22.7) | |
| Asian or Pacific Islander | 376 | 145 (25.4) | 231 (26.2) | |
| Others or unknown | 95 | 41 (7.2) | 54 (6.1) | |
| Educational level | ||||
| <College | 762 | 283 (49.5) | 479 (54.3) | .18 |
| College | 424 | 180 (31.5) | 244 (27.7) | |
| Postgraduate | 268 | 109 (19.1) | 159 (18.0) | |
| Household income, $ | ||||
| <20 000 | 101 | 35 (6.1) | 66 (7.5) | .42 |
| 20 000-40 000 | 253 | 91 (15.9) | 162 (18.4) | |
| >40 000 | 1043 | 423 (74.0) | 620 (70.3) | |
| Marital status | ||||
| Single | 107 | 36 (6.3) | 71 (8.1) | .30 |
| Partner | 187 | 73 (12.8) | 114 (12.9) | |
| Married | 1157 | 463 (80.9) | 694 (78.7) | |
| Smoked since LMP | ||||
| Yes | 137 | 54 (9.4) | 83 (9.4) | .98 |
| No | 1317 | 518 (90.6) | 799 (90.6) | |
| Alcohol use since LMP | ||||
| Yes | 620 | 239 (41.8) | 381 (43.2) | .59 |
| No | 834 | 333 (58.2) | 501 (56.8) | |
| Maternal ADHD history | ||||
| Yes | 14 | 8 (1.4) | 6 (0.7) | .17 |
| No | 1440 | 564 (98.6) | 876 (99.3) | |
| Maternal prepregnancy BMI | ||||
| <25 | 858 | 309 (54.0) | 549 (62.2) | .002 |
| ≥25 | 596 | 263 (46.0) | 333 (37.8) | |
| Preterm delivery | ||||
| Yes | 112 | 41 (7.2) | 71 (8.1) | .56 |
| No | 1335 | 526 (92.3) | 809 (91.9) | |
| Breastfeeding | ||||
| No | 144 | 51 (9.0) | 93 (10.6) | .60 |
| Yes | 1280 | 509 (89.6) | 771 (88.0) | |
| Sex of offspring | ||||
| Male | 755 | 287 (50.2) | 468 (53.1) | .28 |
| Female | 699 | 285 (49.8) | 414 (46.9) | |
| Offspring still enrolled in KPNC at end of study | ||||
| Yes | 995 | 421 (73.6) | 574 (65.1) | .001 |
| No | 459 | 151 (26.4) | 308 (34.9) | |
Abbreviations: ADHD, attention-deficit/hyperactivity disorder; BMI, body mass index (calculated as weight in kilograms divided by height in meters squared); KPNC, Kaiser Permanente Northern California; LMP, last menstrual period; MF, magnetic field.
a
The number in individual categories may not match the total number owing to missing data.
b
The level of MF nonionizing radiation exposure is lower than 1.3 mG.
c
The level of MF nonionizing radiation exposure is 1.3 mG or higher.
d
From χ2 test.