Table 1.
Characteristics of study participants by gestational age at birth (1973–1994), Sweden.
| Early preterm | Late preterm | Early term | Full-term | Post-term | |
|---|---|---|---|---|---|
| (<34 weeks) | (34–36 weeks) | (37–38 weeks) | (39–41 weeks) | (≥42 weeks) | |
| N=21,722 | N=80,183 | N=361,006 | N=1,478,910 | N=199,045 | |
| n (%) | n (%) | n (%) | n (%) | n (%) | |
| Offspring characteristics | |||||
| Sex | |||||
| Male | 11,920 (54.9) | 44,027 (54.9) | 189,294 (52.4) | 750,452 (50.7) | 103,633 (52.1) |
| Female | 9,802 (45.1) | 36,156 (45.1) | 171,712 (47.6) | 728,458 (49.3) | 95,412 (47.9) |
| Birth year | |||||
| 1973–1979 | 5,497 (25.3) | 22,087 (27.5) | 90,517 (25.1) | 453,668 (30.7) | 86,040 (43.2) |
| 1980–1989 | 10,081 (46.4) | 37,661 (47.0) | 171,963 (47.6) | 638,928 (43.2) | 73,413 (36.9) |
| 1990–1994 | 6,144 (28.3) | 20,435 (25.5) | 98,526 (27.3) | 386,314 (26.1) | 39,592 (19.9) |
| Birth order | |||||
| 1 | 10,878 (50.1) | 38,727 (48.3) | 143,703 (39.8) | 605,838 (41.0) | 95,690 (48.1) |
| 2 | 6,146 (28.3) | 24,045 (30.0) | 131,017 (36.3) | 556,883 (37.6) | 66,345 (33.3) |
| ≥3 | 4,698 (21.6) | 17,411 (21.7) | 86,286 (23.9) | 316,189 (21.4) | 37,010 (18.6) |
| Maternal characteristics | |||||
| Age (years) | |||||
| <20 | 1,393 (6.4) | 4,516 (5.6) | 14,673 (4.1) | 57,993 (3.9) | 10,340 (5.2) |
| 20–24 | 5,531 (25.5) | 20,843 (26.0) | 86,189 (23.9) | 376,207 (25.4) | 56,179 (28.2) |
| 25–29 | 6,852 (31.5) | 27,259 (34.0) | 128,622 (35.6) | 563,712 (38.1) | 75,277 (37.8) |
| 30–34 | 4,982 (22.9) | 17,849 (22.3) | 87,613 (24.3) | 345,310 (23.4) | 42,202 (21.2) |
| 35–39 | 2,390 (11.0) | 7,947 (9.9) | 36,027 (10.0) | 116,791 (7.9) | 13,084 (6.6) |
| ≥40 | 574 (2.6) | 1,769 (2.2) | 7,882 (2.2) | 18,897 (1.3) | 1,963 (1.0) |
| Education (years) | |||||
| ≤9 | 4,215 (19.4) | 14,649 (18.3) | 59,633 (16.5) | 220,680 (14.9) | 32,700 (16.4) |
| 10–12 | 11,301 (52.0) | 41,085 (51.2) | 180,946 (50.1) | 736,965 (49.8) | 98,703 (49.6) |
| >12 | 6,206 (28.6) | 24,449 (30.5) | 120,427 (33.4) | 521,265 (35.3) | 67,642 (34.0) |
| Birth country or region | |||||
| Sweden | 18,838 (86.7) | 70,445 (87.9) | 316,185 (87.6) | 1,322,747 (89.4) | 179,536 (90.2) |
| Other Europe/US/Canada | 1,961 (9.0) | 6,622 (8.3) | 28,902 (8.0) | 108,628 (7.4) | 14,307 (7.2) |
| Asia/Oceania | 600 (2.8) | 2,120 (2.6) | 11,096 (3.1) | 31,902 (2.2) | 3,187 (1.6) |
| Africa | 123 (0.6) | 381 (0.5) | 1,725 (0.5) | 6,211 (0.4) | 988 (0.5) |
| Latin America | 113 (0.5) | 437 (0.5) | 2,476 (0.7) | 7,254 (0.5) | 717 (0.4) |
| Other/unknown | 87 (0.4) | 178 (0.2) | 622 (0.2) | 2,168 (0.1) | 310 (0.2) |
| Body mass index (kg/m2) | |||||
| <18.5 | 501 (2.3) | 2,565 (3.2) | 11,433 (3.2) | 36,603 (2.3) | 2,624 (1.3) |
| 18.5–24.9 | 19,898 (91.6) | 72,105 (89.9) | 322,661 (89.4) | 1,341,706 (90.7) | 183,877 (92.4) |
| 25.0–29.9 | 992 (4.6) | 4,265 (5.3) | 21,485 (5.9) | 83,021 (5.6) | 9,906 (5.0) |
| ≥30.0 | 331 (1.5) | 1,248 (1.6) | 5,427 (1.5) | 19,580 (1.3) | 2,638 (1.3) |
| Smoking (cigarettes/day) | |||||
| 0 | 12,665 (58.3) | 48,132 (60.0) | 229,283 (63.5) | 940,499 (63.6) | 115,956 (58.3) |
| 1–9 | 7,155 (32.9) | 25,962 (32.4) | 106,887 (29.6) | 460,183 (31.1) | 75,409 (37.9) |
| ≥10 | 1,902 (8.8) | 6,089 (7.6) | 24,836 (6.9) | 78,228 (5.3) | 7,680 (3.9) |
| Preeclampsia | 3,121 (14.4) | 7,973 (9.9) | 22,974 (6.4) | 66,215 (4.5) | 9,486 (4.8) |
| Other hypertensive disorders | 297 (1.4) | 824 (1.0) | 3,029 (0.8) | 8,285 (0.6) | 806 (0.4) |
| Diabetes mellitus | 631 (2.9) | 2,288 (2.8) | 6,838 (1.9) | 11,742 (0.8) | 1,167 (0.6) |
| Paternal characteristics | |||||
| Age (years) | |||||
| <25 | 3,715 (17.1) | 13,308 (16.6) | 50,393 (14.0) | 211,219 (14.3) | 33,221 16.7) |
| 25–29 | 6,538 (30.1) | 25,608 (31.9) | 114,865 (31.8) | 505,278 (34.2) | 71,051 (35.7) |
| 30–34 | 5,605 (25.8) | 21,697 (27.1) | 105,724 (29.3) | 440,978 (29.8) | 56,008 (28.1) |
| 35–39 | 3,293 (15.2) | 11,646 (14.5) | 56,100 (15.5) | 209,203 (14.1) | 24,783 (12.5) |
| 40–44 | 1,430 (6.6) | 4,701 (5.9) | 21,464 (6.0) | 71,926 (4.9) | 8,549 (4.3) |
| ≥45 | 659 (3.0) | 2,157 (2.7) | 9,160 (2.5) | 29,464 (2.0) | 3,615 (1.8) |
| Unknown | 482 (2.2) | 1,066 (1.3) | 3,300 (0.9) | 10,842 (0.7) | 1,818 (0.9) |
| Education (years) | |||||
| ≤9 | 5,743 (26.4) | 21,109 (26.3) | 89,082 (24.7) | 355,101 (24.0) | 51,383 (25.8) |
| 10–12 | 10,414 (47.9) | 38,407 (47.9) | 172,609 (47.8) | 702,457 (47.5) | 92,574 (46.5) |
| >12 | 5,074 (23.4) | 19,624 (24.5) | 96,114 (26.6) | 410,792 (27.8) | 53,275 (26.8) |
| Unknown | 491 (2.3) | 1,043 (1.3) | 3,201 (0.9) | 10,560 (0.7) | 1,813 (0.9) |