Table 1.
Characteristics of study participants by gestational age at birth, Sweden, 1973–2013.
| Extremely preterm | Very or moderately preterm | Late preterm | Early term | Full-term | Post-term | |
|---|---|---|---|---|---|---|
| (22–27 weeks) | (28–33 weeks) | (34–36 weeks) | (37–38 weeks) | (39–41 weeks) | (≥42 weeks) | |
| N=7,966 (0.2%) | N=42,911 (1.1%) | N=152,824 (3.7%) | N=719,495 (17.6%) | N=2,818,414 (69.1%) | N=338,268 (8.3%) | |
| n (%) | n (%) | n (%) | n (%) | n (%) | n (%) | |
| Child characteristics | ||||||
| Sex | ||||||
| Male | 4,327 (54.3) | 23,914 (55.7) | 83,186 (54.4) | 370,720 (51.5) | 1,431,661 (50.8) | 183,665 (54.3) |
| Female | 3,639 (45.7) | 18,997 (44.3) | 69,638 (45.6) | 348,775 (48.5) | 1,386,753 (49.2) | 154,603 (45.7) |
| Birth order | ||||||
| 1 | 4,033 (50.6) | 22,247 (51.8) | 76,395 (50.0) | 289,701 (40.3) | 1,185,001 (42.0) | 169,260 (50.0) |
| 2 | 2,238 (28.1) | 12,002 (28.0) | 45,344 (29.7) | 263,235 (36.6) | 1,059,293 (37.6) | 108,051 (31.9) |
| ≥3 | 1,695 (21.3) | 8,662 (20.2) | 31,085 (20.3) | 166,559 (23.1) | 574,120 (20.4) | 60,957 (18.0) |
| Maternal characteristics | ||||||
| Age (years) | ||||||
| <20 | 351 (4.4) | 2,039 (4.7) | 6,416 (4.2) | 21,822 (3.0) | 83,174 (2.9) | 12,884 (3.8) |
| 20–24 | 1,522 (19.1) | 8,762 (20.4) | 32,639 (21.4) | 136,535 (19.0) | 570,888 (20.3) | 75,361 (22.3) |
| 25–29 | 2,335 (29.3) | 13,296 (31.0) | 49,865 (32.6) | 237,088 (33.0) | 994,449 (35.3) | 118,844 (35.1) |
| 30–34 | 2,162 (27.1) | 11,394 (26.6) | 40,134 (26.3) | 204,989 (28.5) | 795,092 (28.2) | 90,043 (25.6) |
| 35–39 | 1,256 (15.8) | 5,929 (13.8) | 19,331 (12.6) | 97,092 (13.5) | 317,606 (11.3) | 35,437 (10.5) |
| ≥40 | 340 (4.3) | 1,491 (3.5) | 4,439 (2.9) | 21,969 (3.0) | 57,205 (2.0) | 5,699 (1.7) |
| Education (years) | ||||||
| ≤9 | 1,281 (16.1) | 7,000 (16.3) | 23,537 (15.4) | 100,488 (14.0) | 356,257 (12.6) | 47,313 (14.0) |
| 10–12 | 3,755 (47.1) | 20,361 (47.5) | 72,084 (47.2) | 328,911 (45.7) | 1,269,526 (45.0) | 153,329 (45.3) |
| >12 | 2,809 (35.3) | 15,035 (35.0) | 55,869 (36.6) | 285,065 (39.6) | 1,175,366 (41.7) | 135,261 (40.0) |
| Unknown | 121 (1.5) | 515 (1.2) | 1,334 (0.9) | 5,031 (0.7) | 17,265 (0.6) | 2,365 (0.7) |
| Body mass index (kg/m 2 ) | ||||||
| <18.5 | 137 (1.7) | 1,088 (2.5) | 4,653 (3.0) | 21,206 (2.9) | 63,625 (2.3) | 4,517 (1.3) |
| 18.5–24.9 | 2,160 (27.1) | 13,960 (32.5) | 56,201 (36.8) | 296,688 (41.2) | 1,146,382 (40.7) | 108,829 (32.2) |
| 25.0–29.9 | 968 (12.2) | 5,064 (11.8) | 18,757 (12.3) | 94,759 (13.2) | 362,997 (12.9) | 42,499 (12.6) |
| ≥30.0 | 582 (7.3) | 2,639 (6.2) | 8,863 (5.8) | 40,853 (5.7) | 137,795 (4.9) | 18,580 (5.5) |
| Unknown | 4,119 (51.7) | 20,160 (47.0) | 64,350 (42.1) | 265,989 (37.0) | 1,107,615 (39.3) | 163,843 (48.4) |
| Smoking (cigarettes/day) | ||||||
| 0 | 4,094 (51.4) | 23,260 (54.2) | 88,867 (58.2) | 456,860 (63.5) | 1,758,709 (62.4) | 180,716 (53.4) |
| 1–9 | 717 (9.0) | 4,267 (9.9) | 14,084 (9.2) | 63,674 (8.8) | 214,638 (7.6) | 21,860 (6.5) |
| ≥10 | 493 (6.2) | 2,744 (6.4) | 8,921 (5.8) | 36,642 (5.1) | 111,944 (4.0) | 10,890 (3.2) |
| Unknown | 2,662 (33.4) | 12,640 (29.5) | 40,952 (26.8) | 162,319 (22.6) | 733,123 (26.0) | 124,802 (36.9) |
| Asthma | 1,103 (13.9) | 5,948 (13.9) | 21,363 (14.0) | 94,429 (13.1) | 331,120 (11.8) | 40,189 (11.9) |
| Paternal characteristics | ||||||
| Age (years) | ||||||
| <20 | 572 (7.2) | 5,156 (12.0) | 19,474 (12.7) | 76,449 (10.6) | 306,989 (10.9) | 42,689 (12.6) |
| 20–24 | 1,227 (15.4) | 10,617 (24.7) | 42,670 (27.9) | 194,631 (27.0) | 818,000 (29.0) | 102,961 (30.4) |
| 25–29 | 1,414 (17.7) | 11,200 (26.1) | 43,771 (28.6) | 220,588 (30.7) | 891,131 (31.6) | 102,324 (30.3) |
| 30–34 | 986 (12.4) | 7,094 (16.5) | 25,831 (16.9) | 134,272 (18.7) | 495,406 (17.6) | 54,273 (16.0) |
| 35–39 | 475 (6.0) | 3,123 (7.3) | 10,720 (7.0) | 54,814 (7.6) | 184,293 (6.5) | 20,582 (6.1) |
| ≥40 | 257 (3.2) | 1,573 (3.7) | 5,214 (3.4) | 25,151 (3.5) | 79,642 (2.8) | 9,168 (2.7) |
| Unknown | 3,035 (38.1) | 4,148 (9.7) | 5,144 (3.4) | 13,590 (1.9) | 42,953 (1.5) | 6,271 (1.9) |
| Education (years) | ||||||
| ≤9 | 916 (11.5) | 8,248 (19.2) | 30,891 (20.2) | 137,435 (19.1) | 524,381 (18.6) | 68,985 (20.4) |
| 10–12 | 2,471 (31.0) | 19,256 (44.9) | 73,088 (47.8) | 343,457 (47.7) | 1,331,389 (47.2) | 156,871 (46.4) |
| >12 | 1,540 (19.3) | 11,208 (26.1) | 43,574 (28.5) | 224,465 (31.2) | 917,185 (32.5) | 105,692 (31.2) |
| Unknown | 3,039 (38.2) | 4,199 (9.8) | 5,271 (3.5) | 14,138 (2.0) | 45,459 (1.6) | 6,720 (2.0) |
| Asthma | 425 (5.3) | 3,288 (7.7) | 12,811 (8.4) | 60,126 (8.4) | 229,089 (8.1) | 26.620 (7.9) |