Table 1. Characteristics of Study Participants by Gestational Age at Birth, Sweden, 1973 Through 2014.
| Characteristic | Individuals, No. (%)a | |||||
|---|---|---|---|---|---|---|
| Extremely preterm | Moderately preterm | Late preterm | Early term | Full term | Postterm | |
| Total | 8324 (0.2) | 44 373 (1.1) | 157 342 (3.7) | 740 391 (17.7) | 2 896 444 (69.1) | 346 195 (8.3) |
| Child characteristics | ||||||
| Sex | ||||||
| Male | 4529 (54.4) | 24 734 (55.7) | 85 570 (54.4) | 381 140 (51.5) | 1 471 368 (50.8) | 188 358 (54.4) |
| Female | 3795 (45.6) | 19 639 (44.3) | 71 772 (45.6) | 359 251 (48.5) | 1 425 076 (49.2) | 157 837 (45.6) |
| Fetal growthb | ||||||
| Small for gestational age | 73 (0.9) | 5630 (12.7) | 15 623 (9.9) | 54 405 (7.3) | 276 687 (9.6) | 66 724 (19.3) |
| Appropriate for gestational age | 8015 (96.3) | 37 019 (83.4) | 128 530 (81.7) | 601 039 (81.2) | 2 326 431 (80.3) | 253 586 (73.2) |
| Large for gestational age | 236 (2.8) | 1724 (3.9) | 13 189 (8.4) | 84 947 (11.5) | 293 326 (10.1) | 25 885 (7.5) |
| Birth order | ||||||
| 1 | 4140 (49.7) | 22 780 (51.3) | 78 019 (49.6) | 297 655 (40.2) | 1 219 056 (42.1) | 172 702 (49.9) |
| 2 | 2384 (28.6) | 12 525 (28.2) | 47 050 (29.9) | 271 130 (36.6) | 1 087 624 (37.5) | 111 055 (32.1) |
| ≥3 | 1800 (21.6) | 9068 (20.4) | 32 273 (20.5) | 171 606 (23.2) | 589 764 (20.4) | 62 438 (18.0) |
| Patent ductus arteriosus | 75 (0.9) | 79 (0.2) | 82 (<0.1) | 196 (<0.1) | 563 (<0.1) | 77 (<0.1) |
| Other circulatory anomalies | 126 (1.5) | 617 (1.4) | 1179 (0.8) | 3430 (0.5) | 8557 (0.3) | 1100 (0.3) |
| Noncirculatory anomalies | 505 (6.1) | 2598 (5.9) | 7560 (4.8) | 32 759 (4.4) | 128 656 (4.4) | 15 081 (4.4) |
| Family history of heart failure | 244 (2.9) | 2089 (4.7) | 7227 (4.6) | 27 941 (3.8) | 102 454 (3.5) | 15 067 (4.4) |
| Family history of ischemic heart disease | 467 (5.6) | 4058 (9.2) | 14 620 (9.3) | 60 596 (8.2) | 227 023 (7.8) | 32 697 (9.4) |
| Maternal characteristics | ||||||
| Age, y | ||||||
| <20 | 356 (4.3) | 2058 (4.6) | 6476 (4.1) | 22 069 (3.0) | 84 019 (2.9) | 12 962 (3.7) |
| 20-24 | 1575 (18.9) | 8957 (20.2) | 33 190 (21.1) | 139 115 (18.8) | 580 841 (20.0) | 76 287 (22.0) |
| 25-29 | 2436 (29.3) | 13 725 (30.9) | 51 191 (32.5) | 243 257 (32.9) | 1 018 871 (35.2) | 121 285 (35.0) |
| 30-34 | 2271 (27.3) | 11 831 (26.7) | 41 555 (26.4) | 211 859 (28.6) | 821 668 (28.4) | 92 813 (26.8) |
| 35-39 | 1314 (15.8) | 6199 (14.0) | 20 167 (12.8) | 100 963 (13.6) | 330 847 (11.4) | 36 883 (10.7) |
| ≥40 | 372 (4.5) | 1603 (3.6) | 4763 (3.0) | 23 128 (3.1) | 60 198 (2.1) | 5965 (1.7) |
| Education, y | ||||||
| ≤9 | 1401 (16.8) | 7322 (16.5) | 24 405 (15.5) | 104 171 (14.1) | 367 829 (12.7) | 48 594 (14.0) |
| 10-12 | 3920 (47.1) | 21 112 (47.6) | 74 269 (47.2) | 338 702 (45.7) | 1 304 778 (45.0) | 157 018 (45.4) |
| >12 | 3003 (36.1) | 15 939 (35.9) | 58 668 (37.3) | 297 518 (40.2) | 1 223 837 (42.3) | 140 583 (40.6) |
| Birth country or region | ||||||
| Sweden | 6379 (76.6) | 36 271 (81.7) | 130 227 (82.8) | 603 828 (81.6) | 2 424 626 (83.7) | 294 280 (85.0) |
| Another European country, US, or Canada | 873 (10.5) | 3879 (8.7) | 13 239 (8.4) | 62 313 (8.4) | 236 119 (8.2) | 27 999 (8.1) |
| Asia or Oceania | 618 (7.4) | 2548 (5.7) | 9108 (5.8) | 50 443 (6.8) | 150 854 (5.2) | 11 962 (3.5) |
| Africa | 251 (3.0) | 811 (1.8) | 2055 (1.3) | 10 868 (1.5) | 46 094 (1.6) | 8025 (2.3) |
| Latin America | 92 (1.1) | 389 (0.9) | 1522 (1.0) | 8476 (1.1) | 24 158 (0.8) | 2014 (0.6) |
| Other/unknown | 111 (1.3) | 475 (1.1) | 1191 (0.8) | 4463 (0.6) | 14 593 (0.5) | 1915 (0.5) |
| BMI | ||||||
| <18.5 | 140 (1.7) | 1146 (2.6) | 4808 (3.1) | 21 784 (2.9) | 65 600 (2.3) | 4649 (1.3) |
| 18.5-24.9 | 6111 (73.4) | 34 215 (77.1) | 121,37 (77.1) | 567 018 (76.6) | 2 279 549 (78.7) | 275 218 (79.5) |
| 25.0-29.9 | 1456 (17.5) | 6189 (13.9) | 21 663 (13.8) | 107 959 (14.6) | 404 340 (14.0) | 46 600 (13.5) |
| ≥30.0 | 617 (7.4) | 2823 (6.4) | 9534 (6.1) | 43 630 (5.9) | 146 991 (5.1) | 19 728 (5.7) |
| Smoking, cigarettes/d | ||||||
| 0 | 6091 (73.2) | 31 407 (70.8) | 114 671 (72.9) | 565 076 (76.3) | 2 216 387 (76.5) | 247 302 (71.4) |
| 1-9 | 1737 (20.9) | 10 211 (23.0) | 33 688 (21.4) | 138 352 (18.7) | 567 341 (19.6) | 87 934 (25.4) |
| ≥10 | 496 (6.0) | 2755 (6.2) | 8983 (5.7) | 36 963 (5.0) | 112 716 (3.9) | 10 959 (3.2) |
| Preeclampsia | 1032 (12.4) | 7869 (17.7) | 16 095 (10.2) | 39 382 (5.3) | 94 720 (3.3) | 11 833 (3.4) |
| Other hypertensive disorders | 111 (1.3) | 790 (1.8) | 2241 (1.4) | 8897 (1.2) | 24 746 (0.9) | 2347 (0.7) |
| Diabetes | 238 (2.9) | 1650 (3.7) | 6151 (3.9) | 19 121 (2.6) | 31 304 (1.1) | 2260 (0.7) |
Abbreviation: BMI, body mass index (calculated as weight in kilograms divided by height in meters squared).
a
Preterm birth was defined as any at a gestational age less than 37 weeks; extremely preterm, at 22 to 27 weeks’ gestational age; moderately preterm, at 28 to 33 weeks’ gestational age; late preterm, at 34 to 36 weeks’ gestational age; early term, at 37 to 38 weeks’ gestational age; full term, at 39 to 41 weeks’ gestational age; and postterm, at 42 weeks’ gestational age or more.
b
Small for gestational age was defined as a weight less than the 10th percentile; appropriate for gestational age, between the 10th and 90th percentiles; and large for gestational age, greater than the 99th percentile.