Table 1.
Characteristics of study participants by shortest pregnancy duration, Sweden, 1973–2015.
| Extremely preterm | Very preterm | Late preterm | Early term | Full-term | Post-term | |
|---|---|---|---|---|---|---|
| (22–27 wks) | (28–33 wks) | (34–36 wks) | (37–38 wks) | (39–41 wks) | (≥42 wks) | |
| N=9,100 | N=45,438 | N=140,213 | N=551,741 | N=1,353,180 | N=89,518 | |
| n (%) | n (%) | n (%) | n (%) | n (%) | n (%) | |
| Age at first delivery (yrs) | ||||||
| <20 | 806 (8.9) | 4,123 (9.1) | 11,400 (8.1) | 35,948 (6.5) | 64,181 (4.7) | 2,811 (3.1) |
| 20–24 | 2,584 (28.4) | 13,332 (29.3) | 42,385 (30.2) | 162,323 (29.4) | 364,039 (26.9) | 17,758 (19.8) |
| 25–29 | 2,774 (30.5) | 14,585 (32.1) | 47,275 (33.7) | 194,606 (35.3) | 498,601 (36.9) | 31,064 (34.7) |
| 30–34 | 1,873 (20.6) | 9,048 (19.9) | 27,458 (19.6) | 112,822 (20.4) | 304,770 (22.5) | 24,746 (27.6) |
| 35–39 | 855 (9.4) | 3,502 (7.7) | 9,652 (6.9) | 37,791 (6.9) | 101,781 (7.5) | 11,045 (12.3) |
| ≥40 | 208 (2.3) | 848 (1.9) | 2,043 (1.5) | 8,251 (1.5) | 19,808 (1.5) | 2,094 (2.3) |
| Year of delivery | ||||||
| 1973–1979 | 1,445 (15.9) | 10,134 (22.3) | 31,067 (22.2) | 112,447 (20.4) | 338,107 (25.0) | 33,920 (37.9) |
| 1980–1989 | 1,772 (19.5) | 10,759 (23.7) | 33,784 (24.1) | 126,372 (22.9) | 258,777 (19.1) | 11,880 (13.3) |
| 1990–1999 | 1,992 (21.9) | 10,003 (22.0) | 30,431 (21.7) | 121,692 (22.1) | 267,620 (19.8) | 12,206 (13.6) |
| 2000–2009 | 2,240 (24.6) | 9,329 (20.5) | 29,148 (20.8) | 126,479 (22.9) | 279,231 (20.6) | 12,955 (14.5) |
| 2010–2015 | 1,651 (18.1) | 5,213 (11.5) | 15,783 (11.3) | 64,751 (11.7) | 209,445 (15.5) | 18,557 (20.7) |
| Final parity | ||||||
| 1 | 1,726 (19.0) | 8,353 (18.4) | 23,567 (16.8) | 86,307 (15.6) | 326,647 (24.1) | 46,394 (51.8) |
| 2 | 3,069 (33.7) | 18,074 (39.8) | 62,524 (44.6) | 263,457 (47.8) | 669,663 (49.5) | 29,684 (33.2) |
| 3 | 2,500 (27.5) | 11,456 (25.2) | 34,755 (24.8) | 140,344 (25.4) | 269,088 (19.9) | 9,983 (11.2) |
| 4 | 1,126 (12.4) | 4,746 (10.4) | 12,656 (9.0) | 42,722 (7.7) | 64,300 (4.8) | 2,432 (2.7) |
| ≥5 | 678 (7.4) | 2,809 (6.2) | 6,711 (4.8) | 18,991 (3.4) | 23,482 (1.7) | 1,025 (1.1) |
| Education (years) | ||||||
| ≤9 | 1,509 (16.6) | 7,494 (16.5) | 21,398 (15.3) | 75,831 (13.7) | 181,799 (13.4) | 16,092 (18.0) |
| 10–12 | 4,215 (46.3) | 21,517 (47.4) | 65,445 (46.7) | 247,684 (44.9) | 591,354 (43.7) | 38,871 (43.3) |
| >12 | 3,376 (37.1) | 16,427 (36.1) | 53,370 (38.1) | 228,226 (41.4) | 580,027 (42.9) | 34,645 (38.7) |
| Employment Income (quartile) | 7,524 (82.7) | 38,283 (84.3) | 120,050 (85.6) | 474,773 (86.0) | 1,173,672 (86.7) | 75,523 (84.4) |
| 1st (highest) | 2,497 (27.4) | 10,391 (22.9) | 31,246 (22.3) | 131,154 (23.8) | 348,887 (25.8) | 24,442 (27.3) |
| 2nd | 2,224 (24.4) | 10,724 (23.6) | 33,572 (23.9) | 132,303 (24.0) | 342,011 (25.3) | 25,361 (28.3) |
| 3rd | 1,910 (21.0) | 11,604 (25.5) | 35,897 (25.6) | 138,540 (25.1) | 338,997 (25.1) | 22,460 (25.1) |
| 4th (lowest) | 2,469 (27.1) | 12,719 (28.0) | 39,498 (28.2) | 149,744 (27.1) | 323,285 (23.9) | 17,255 (19.3) |
| Birth country or region | ||||||
| Sweden | 6,953 (76.4) | 37,435 (82.4) | 116,268 (82.9) | 449,450 (81.5) | 1,114,560 (82.4) | 72,314 (80.8) |
| Other Europe/US/Canada | 963 (10.6) | 3,975 (8.8) | 12,124 (8.7) | 48,847 (8.9) | 128,982 (9.5) | 10,412 (11.6) |
| Asia/Oceania | 741 (8.1) | 2,670 (5.9) | 8,358 (6.0) | 38,257 (6.9) | 73,884 (5.5) | 3,702 (4.1) |
| Africa | 326 (3.6) | 901 (2.0) | 1,932 (1.4) | 8,161 (1.5) | 21,729 (1.6) | 2,211 (2.5) |
| Latin America | 108 (1.2) | 398 (0.9) | 1,392 (1.0) | 6,484 (1.2) | 12,656 (0.9) | 759 (0.9) |
| Other/unknown | 9 (0.1) | 59 (0.1) | 139 (1.0) | 542 (0.1) | 1,369 (0.1) | 120 (0.1) |
| Body mass index (kg/m2) | ||||||
| <18.5 | 223 (2.5) | 1,292 (2.8) | 4,215 (3.0) | 16,244 (2.9) | 29,739 (2.2) | 1,048 (1.2) |
| 18.5–24.9 | 6,921 (76.0) | 36,692 (80.8) | 114,028 (81.3) | 450,446 (81.6) | 1,110,017 (82.0) | 72,130 (80.6) |
| 25.0–29.9 | 1,350 (14.8) | 5,171 (11.4) | 15,665 (11.2) | 62,517 (11.3) | 158,259 (11.7) | 11,213 (12.5) |
| ≥30.0 | 606 (6.7) | 2,283 (5.0) | 6,305 (4.5) | 22,534 (4.1) | 55,165 (4.1) | 5,127 (5.7) |
| Smoking (cigarettes/day) | ||||||
| 0 | 6,597 (72.5) | 31,241 (68.8) | 99,871 (71.2) | 410,313 (74.4) | 992,881 (73.4) | 57,914 (64.7) |
| 1–9 | 2,061 (22.6) | 12,036 (26.5) | 34,519 (24.6) | 121,529 (22.0) | 312,931 (23.8) | 29,576 (33.0) |
| ≥10 | 442 (4.9) | 2,161 (4.8) | 5,823 (4.2) | 19,899 (3.6) | 38,368 (2.8) | 2,028 (2.3) |
| Preeclampsia | 1,028 (11.3) | 6,995 (15.4) | 14,159 (10.1) | 35,697 (6.5) | 61,307 (4.5) | 4,100 (4.6) |
| Other hypertensive disorders | 102 (1.1) | 681 (1.5) | 1,755 (1.3) | 6,224 (1.1) | 12,614 (0.9) | 738 (0.8) |
| Diabetes mellitus | 213 (2.3) | 1,386 (3.1) | 4,312 (3.1) | 9,981 (1.8) | 11,097 (0.8) | 476 (0.5) |