Table 1.
Baseline characteristics of the study participants and maternal occupational noise exposure during pregnancy [n (%)].
| Characteristics | Occupational noise exposurea | ||
|---|---|---|---|
| < 75 dBA | 75–84 dBA | ≥ 85 dBA | |
| n total sample (1,422,333) | 1,126,356 | 290,071 | 5,906 |
| Mother’s characteristics | |||
| Age (quartiles) | |||
| ≤ 24 years | 175,994 (15.6) | 59,519 (20.5) | 1,498 (25.4) |
| 25–28 years | 311,072 (27.6) | 86,938 (30.0) | 1,671 (28.3) |
| 29–32 years | 336,334 (29.9) | 79,124 (27.3) | 1,430 (24.2) |
| ≥ 33 years | 302,956 (26.9) | 64,490 (22.2) | 1,307 (22.1) |
| Missing | 0 (0) | 0 (0) | 0 (0) |
| Smoking | |||
| Nonsmokers | 938,088 (85.9) | 225,991 (80.5) | 4,434 (77.3) |
| Smokers, 1–9 cig per day | 105,229 (9.6) | 34,062 (12.1) | 756 (13.2) |
| Smokers, ≥ 10 cig per day | 49,190 (4.5) | 20,549 (7.3) | 545 (9.5) |
| Missing | 33,849 (3.0) | 9,469 (3.3) | 171 (2.9) |
| Highest completed educational level | |||
| Pre-high school | 96,232 (8.7) | 52,666 (18.7) | 1,222 (21.3) |
| High school | 610,581 (54.9) | 133,051 (47.2) | 3,593 (62.7) |
| University < 3 years | 151,663 (13.6) | 70,206 (24.9) | 323 (5.6) |
| University ≥ 3 years | 254,089 (22.8) | 25,840 (9.2) | 593 (10.4) |
| Missing | 13,791 (1.2) | 8,308 (2.9) | 175 (3.0) |
| Nationality | |||
| Swedish | 1,047,984 (93.1) | 257,149 (88.7) | 5,348 (90.6) |
| Other European country | 39,513 (3.5) | 15,089 (5.2) | 314 (5.3) |
| Outside Europe | 16,682 (1.5) | 9,445 (3.3) | 99 (1.7) |
| Unknown | 22,030 (2.0) | 8,306 (2.9) | 144 (2.4) |
| Missing | 147 (0) | 82 (0) | 1 (0) |
| Working at beginning of pregnancyb | |||
| No | 59,881 (5.9) | 14,312 (5.5) | 292 (5.4) |
| Part time | 377,291 (37.2) | 91,079 (35.2) | 1,251 (23.3) |
| Full time | 576,487 (56.9) | 153,186 (59.2) | 3,824 (71.3) |
| Missing | 112,697 (10.0) | 31,494 (10.9) | 539 (9.1) |
| Leave of absencec | |||
| < 20 days | 515,358 (45.8) | 106,403 (36.7) | 1,845 (31.2) |
| 20–153 days | 513,628 (45.6) | 151,814 (52.3) | 3,214 (54.4) |
| > 153 days | 97,370 (8.6) | 31,854 (11.0) | 847 (14.3) |
| Missing | 0 (0) | 0 (0) | 0 (0) |
| Family structure | |||
| Married/living together with the father | 1,052,832 (96.4) | 266,783 (95.1) | 5,490 (96.0) |
| Missing | 34,455 (3.1) | 9,563 (3.3) | 186 (3.1) |
| Child’s characteristics | |||
| Sex | |||
| Male | 578,886 (51.4) | 149,087 (51.4) | 2,986 (50.6) |
| Missing | 0 (0) | 0 (0) | 0 (0) |
| Parity | |||
| 1 | 500,459 (44.4) | 119,747 (41.3) | 2,596 (44.0) |
| 2 | 413,151 (36.7) | 103,068 (35.5) | 2,035 (34.5) |
| ≥ 3 | 212,746 (18.9) | 67,256 (23.2) | 1,275 (21.6) |
| Missing | 0 (0) | 0 (0) | 0 (0) |
| Birth year | |||
| 1986–1990 | 258,479 (23.0) | 86,280 (29.7) | 1,439 (24.4) |
| 1991–1996 | 318,963 (28.3) | 87,659 (30.2) | 1,871 (31.7) |
| 1997–2002 | 245,798 (21.8) | 57,062 (19.7) | 1,315 (22.3) |
| 2003–2008 | 303,116 (26.9) | 59,070 (20.4) | 1,281 (21.7) |
| Missing | 0 (0) | 0 (0) | 0 (0) |
| aOccupational noise exposure estimated through a job–exposure matrix based on measurements at several work sites, subdividing the mother’s occupation registered at the beginning of the pregnancy into three noise categories. bIncludes mothers who had reported an occupation at the beginning of pregnancy (gestational week 10), and divides them according to their answer on the separate presence-at-work-question (Do you work right now? no/part time/full time). cNumber of days of leave of absence due to sick leave or parental leave reported to the Social Insurance Agency register during pregnancy, including a summation of all days between the conception date (birthdate – days of gestation = conception date) and the birth date. Cut-off was at the median level 20 days and at 153 days of absence, equivalent to the 90th percentile. | |||