Table 1. Characteristics of mothers and children in study population, by fever exposure status and diagnosis.
| Subject characteristics | All subjects (N=95 754) | Any fever (N=15 701) | No fever (N=80 053) | ASD (N=583) | Non-case (N=95 171) | P-valuea |
|---|---|---|---|---|---|---|
| Parental characteristics | ||||||
| Maternal age (years), N (%) | <0.0001 | |||||
| <20 | 971 (1.0) | 180 (1.1) | 791 (1.0) | 10 (1.7) | 961 (1.0) | |
| 20−24 | 9691 (10.1) | 1605 (10.2) | 8086 (10.1) | 94 (16.1) | 9597 (10.1) | |
| 25−29 | 31 597 (33.0) | 5174 (33.0) | 26 423 (33.0) | 191 (32.8) | 31 406 (33.0) | |
| 30−34 | 36 893 (38.5) | 6090 (38.8) | 30 803 (38.5) | 188 (32.2) | 36 705 (38.6) | |
| 35−39 | 14 701 (15.4) | 2356 (15.0) | 12345 (15.4) | 91 (15.6) | 14 610 (15.4) | |
| ⩾40 | 1901 (2.0) | 296 (1.9) | 1605 (2.0) | 9 (1.5) | 1892 (2.0) | |
| Parental education, N (%) | <0.0001 | |||||
| <12 years | 3261 (3.4) | 444 (2.8) | 2817 (3.5) | 41 (7.0) | 3220 (3.4) | |
| 12 years | 21 862 (22.8) | 3325 (21.2) | 18 537 (23.2) | 171 (29.3) | 21 691 (22.8) | |
| 13−16 years | 36 168 (37.8) | 5964 (38.0) | 30 204 (37.7) | 203 (34.8) | 35 965 (37.8) | |
| ⩾17 years | 33 033 (34.5) | 5737 (36.5) | 27 266 (34.1) | 160 (27.4) | 32 843 (34.5) | |
| Missingb | 1460 (1.5) | 231 (1.5) | 1229 (1.5) | 8 (1.4) | 1452 (1.5) | |
| Maternal smoking, N (%) | <0.0001 | |||||
| Yes | 8965 (9.4) | 1490 (9.5) | 7 475 (9.3) | 89 (15.3) | 8876 (9.3) | |
| No | 68 929 (72.0) | 11 843 (75.4) | 57 086 (71.3) | 385 (66.0) | 68 544 (72.0) | |
| Missingb | 17 860 (18.7) | 2368 (15.1) | 15 492 (19.4) | 109 (18.7) | 17 751 (18.7) | |
| Parity, N (%) | <0.0001 | |||||
| 0 | 42 412 (44.3) | 6377 (40.6) | 36 035 (45.0) | 319 (54.7) | 42 093 (44.2) | |
| ⩾1 | 53 342 (55.7) | 9324 (59.4) | 44 018 (55.0) | 264 (45.3) | 53 078 (55.8) | |
| Mode of delivery, N (%) | 0.065 | |||||
| Spontaneous | 77 472 (80.9) | 12 604 (80.3) | 64 868 (81.0) | 450 (77.2) | 77 022 (80.9) | |
| Induced | 12 339 (12.9) | 2085 (13.3) | 10 254 (12.8) | 92 (15.8) | 12 247 (12.9) | |
| Cesarean section | 5943 (6.2) | 1012 (6.4) | 4931 (6.2) | 41 (7.0) | 5902 (6.2) | |
| Child characteristics | ||||||
| Sex, N (%) | <0.0001 | |||||
| Male | 49 197 (51.4) | 8030 (51.1) | 41 167 (51.4) | 487 (83.5) | 48 710 (51.2) | |
| Female | 46 557 (48.6) | 7671 (48.9) | 38 886 (48.6) | 96 (16.5) | 46 461 (48.8) | |
| Gestational age, N (%) | 0.002 | |||||
| 32−36 weeks | 2552 (2.7) | 431 (2.7) | 2121 (2.6) | 23 (3.9) | 2529 (2.7) | |
| 37−38 weeks | 15 301 (16.0) | 2602 (16.6) | 12 699 (15.9) | 98 (16.8) | 15 203 (16.0) | |
| 39−41 weeks | 70 202 (73.3) | 11 420 (72.7) | 58 782 (73.4) | 395 (67.8) | 69 807 (73.3) | |
| ⩾42 weeks | 7 699 (8.0) | 1248 (7.9) | 6451 (8.1) | 67 (11.5) | 7632 (8.0) | |
| Birth weight (g), mean (s.d.) | 0.009 | |||||
| 2500−2999 | 8 378 (8.7) | 1323 (8.4) | 7055 (8.8) | 68 (11.7) | 8310 (8.7) | |
| 3000−3499 | 28 519 (29.8) | 4703 (30.0) | 23 816 (29.8) | 155 (26.6) | 28 364 (29.8) | |
| 3500−3999 | 36 779 (38.4) | 6025 (38.4) | 30 754 (38.4) | 205 (35.2) | 36 574 (38.4) | |
| 4000−4499 | 17 648 (18.4) | 2935 (18.7) | 14 713 (18.4) | 119 (20.4) | 17 529 (18.4) | |
| ⩾4500 | 4430 (4.6) | 715 (4.6) | 3715 (4.6) | 36 (6.2) | 4394 (4.6) | |
| Birth year, N (%) | <0.0001 | |||||
| 1999 | 35 (0.0) | 0 (0.0) | 35 (0.0) | 1 (0.2) | 34 (0.0) | |
| 2000 | 1859 (1.9) | 261 (1.7) | 1598 (2.0) | 17 (2.9) | 1842 (1.9) | |
| 2001 | 3670 (3.8) | 597 (3.8) | 3073 (3.8) | 38 (6.5) | 3632 (3.8) | |
| 2002 | 7713 (8.1) | 1159 (7.4) | 6554 (8.2) | 87 (14.9) | 7626 (8.0) | |
| 2003 | 11 220 (11.7) | 1640 (10.4) | 9580 (12.0) | 110 (18.9) | 11 110 (11.7) | |
| 2004 | 12 091 (12.6) | 1992 (12.7) | 10 099 (12.6) | 83 (14.2) | 12 008 (12.6) | |
| 2005 | 14 024 (14.6) | 2373 (15.1) | 11 651 (14.6) | 86 (14.8) | 13 938 (14.6) | |
| 2006 | 15 707 (16.4) | 2509 (16.0) | 13 198 (16.5) | 60 (10.3) | 15 647 (16.4) | |
| 2007 | 14 387 (15.0) | 2654 (16.9) | 11 733 (14.7) | 53 (9.1) | 14 334 (15.1) | |
| 2008 | 12 001 (12.5) | 1958 (12.5) | 10 043 (12.5) | 41 (7.0) | 11 960 (12.6) | |
| 2009 | 3047 (3.2) | 558 (3.6) | 2489 (3.1) | 7 (1.2) | 3040 (3.2) | |
| Birth month, N (%) | 0.156 | |||||
| January | 7979 (8.3) | 1000 (6.4) | 6979 (8.7) | 48 (8.2) | 7931 (8.3) | |
| February | 7661 (8.0) | 1105 (7.0) | 6556 (8.2) | 51 (8.7) | 7610 (8.0) | |
| March | 8610 (9.0) | 1446 (9.2) | 7164 (8.9) | 52 (10.7) | 8558 (9.0) | |
| April | 8642 (9.0) | 1611 (10.3) | 7031 (8.8) | 62 (10.6) | 8580 (9.0) | |
| May | 8567 (8.9) | 1820 (11.6) | 6747 (8.4) | 47 (8.1) | 8520 (9.0) | |
| June | 8024 (8.4) | 1750 (11.1) | 6274 (7.8) | 43 (7.4) | 7981 (8.4) | |
| July | 8800 (9.2) | 1666 (10.6) | 7134 (8.9) | 39 (6.7) | 8761 (9.2) | |
| August | 8386 (8.8) | 1488 (9.5) | 6898 (8.6) | 37 (6.3) | 8349 (8.8) | |
| September | 8037 (8.4) | 1211 (7.7) | 6826 (8.5) | 53 (9.1) | 7984 (8.4) | |
| October | 7700 (8.0) | 980 (6.2) | 6720 (8.4) | 55 (9.4) | 7645 (8.0) | |
| November | 6763 (7.1) | 829 (5.3) | 5934 (7.4) | 40 (6.9) | 6723 (7.1) | |
| December | 6585 (6.9) | 795 (5.1) | 5790 (7.2) | 47 (8.1) | 6538 (6.9) | |
| ASD, N (%) | 583 (0.6) | 113 (0.7) | 470 (0.6) | |||
| Non-case, N (%) | 95 171 (99.4) | 15 588 (99.3) | 79 583 (99.4) | |||
Abbreviation: ASD, autism spectrum disorder.
Key: g, grams.
a
P-values are those associated with χ2-tests comparing prevalence of each characteristic in the ASD and non-case groups.
b
Missing data imputed for subsequent analyses (Supplementary Methods).