Table 1.
Characteristics of the Stockholm Youth Cohort, born 1984–2007.
| Characteristics | No ASD (N = 470,703) | ASD (N = 10,025) | ASD without ID (N = 7,657) | ASD with ID (N = 2,368) |
|---|---|---|---|---|
| Male, n (%) | 239330 (50.8) | 7103 (70.9) | 5406 (70.6) | 1697 (71.7) |
| Birthweight-for-gestational age z-score, mean (SD a) | 0 (1) | −0.1 (1.1) | 0 (1.1) | −0.2 (1.2) |
| Maternal age (years) at delivery, mean (SD) | 29.8 (5.2) | 29.7 (5.5) | 29.7 (5.5) | 29.8 (5.6) |
| Paternal age (years) at delivery, mean (SD) | 32.8 (6.3) | 32.8 (6.7) | 32.5 (6.6) | 33.5 (6.9) |
| Gestational age at birth b, n (%) | ||||
| Extremely preterm (<28 weeks) | 580 (0.1) | 49 (0.5) | 28 (0.4) | 21 (0.9) |
| Very preterm (28 – <32 weeks) | 1193 (0.2) | 51 (0.5) | 34 (0.4) | 17 (0.7) |
| Moderate to late preterm (32 – <37 weeks) | 18943 (4.0) | 541 (5.4) | 397 (5.2) | 144 (6.1) |
| Term (37 – <42 weeks) | 413721 (87.9) | 8458 (85.2) | 6577 (85.9) | 1971 (83.2) |
| Postterm (≥42 weeks) | 36386 (7.7) | 840 (8.4) | 624 (8.1) | 216 (9.1) |
| Parity, n (%) | ||||
| 1 | 211913 (45.0) | 4863 (48.5) | 3866 (50.5) | 997 (42.1) |
| 2 | 170729 (36.3) | 3299 (32.9) | 2451 (32.0) | 848 (35.8) |
| ≥3 | 88061 (18.7) | 1863 (18.6) | 1340 (17.5) | 523 (22.1) |
| Gestational hypertension, n (%) | 14140 (3.0) | 424 (4.2) | 345 (4.5) | 79 (3.3) |
| Gestational diabetes, n (%) | 2986 (0.6) | 110 (1.1) | 80 (1.0) | 30 (1.3) |
| Maternal smoking during pregnancy c, n (%) | 65867 (14.0) | 1634 (16.3) | 1298 (17.0) | 336 (14.2) |
| Maternal neuropsychiatric history, n (%) | 29773 (6.3) | 916 (9.1) | 741 (9.7) | 175 (7.4) |
| Paternal neuropsychiatric history, n (%) | 22096 (4.7) | 666 (6.6) | 526 (6.9) | 140 (5.9) |
| Family income, n (%) | ||||
| Q1 (Lowest) | 68602 (14.6) | 1585 (15.8) | 1072 (14.0) | 513 (21.7) |
| Q2 | 73429 (15.6) | 1835 (18.3) | 1371 (17.9) | 464 (19.6) |
| Q3 | 74611 (15.9) | 1810 (18.1) | 1423 (18.6) | 387 (16.3) |
| Q4 | 94207 (20.0) | 1976 (19.7) | 1581 (20.7) | 395 (16.7) |
| Q5 (Highest) | 159854 (34.0) | 2819 (28.1) | 2210 (28.9) | 609 (25.7) |
| Maternal region of origin, n (%) | ||||
| Born in Sweden | 358164 (76.1) | 7743 (77.2) | 6191 (80.9) | 1552 (65.5) |
| Born in Europe outside Sweden | 39276 (8.3) | 895 (8.9) | 657 (8.6) | 238 (10.1) |
| Born outside Europe | 73263 (15.6) | 1387 (13.8) | 809 (10.6) | 578 (24.4) |
| Birth year d, n (%) | ||||
| 1984 – 1988 | 83504 (98.5) | 1249 (1.5) | 890 (1.1) | 359 (0.4) |
| 1989 – 1993 | 108302 (97.8) | 2474 (2.2) | 1816 (1.6) | 658 (0.6) |
| 1994 – 1998 | 94569 (97.1) | 2871 (2.9) | 2206 (2.3) | 665 (0.6) |
| 1999 – 2003 | 94486 (97.7) | 2266 (2.3) | 1814 (1.9) | 452 (0.4) |
| 2004 – 2007 | 89842 (98.7) | 1165 (1.3) | 931 (1.0) | 234 (0.3) |
a.
SD: standard deviation.
b.
The minimum and maximum gestational age at birth was 23 and 45 weeks, respectively.
c.
10.7% and 11.0% of maternal self-reported smoking during pregnancy data were missing among individuals with and without ASD diagnosis, respectively.
d.
Birth year was summarized in this table as birth year intervals and included in the GAM model as a continuous variable. Column-wise proportions were calculated to present prevalence of ASD with and without ID over birth year periods.