Table 1 Maternal characteristics and pregnancy outcomes among women delivering between 1973 and 2012 in Sweden, stratified by exposure to preterm delivery before 37 weeks (n = 1,943,716)
|  | No preterm delivery, n (%) N = 1,780,798 (91.6) | Preterm delivery, n (%) N = 162,918 (8.4) |
|---|---|---|
Age in years | ||
 < 20 | 97,007 (5.5) | 14,384 (8.8) |
 20–29 | 1,151,931 (64.7) | 104,337 (64.0) |
 30–39 | 507,226 (28.5) | 41,921 (25.7) |
 ≥ 40 | 24,634 (1.4) | 2276 (1.4) |
Native country | ||
 Sweden | 1,509,135 (84.7) | 138,441 (85.0) |
 Elsewhere | 271,663 (15.3) | 24,477 (15.0) |
Education level | ||
 Less than upper secondary | 233,341 (13.1) | 24,540 (15.1) |
 Upper secondary | 800,419 (45.0) | 77,826 (47.8) |
 Third level | 709,299 (39.8) | 57,702 (35.4) |
 Missing | 37,739 (2.1) | 2850 (1.8) |
Body mass index in early pregnancy (kg/m2) | ||
 Underweight, < 18.5 | 41,129 (2.3) | 4830 (3.0) |
 Normal, 18.5–24.9 | 655,619 (36.8) | 55,415 (34.0) |
 Overweight, 25–29.9 | 178,593 (10.0) | 15,447 (9.5) |
 Obese, ≥ 30 | 64,011 (3.6) | 6445 (4.0) |
 Missing | 841,446 (47.3) | 80,781 (49.6) |
Maternal smoking | ||
 No | 950,672 (53.4) | 83,138 (51.0) |
 Yes | 187,197 (10.5) | 21,404 (13.1) |
 Missing | 642,929 (36.1) | 58,376 (35.8) |
Gestational diabetes (ever) | ||
 No | 1,764,968 (99.1) | 160,133 (98.3) |
 Yes | 15,830 (0.9) | 2785 (1.7) |
Preeclampsia (ever) | ||
 No | 1,709,392 (96.0) | 141,702 (87.0) |
 Yes | 71,406 (4.0) | 21,216 (13.0) |
Small for gestational age (SGA) (ever) | ||
 No | 1,700,028 (95.6) | 140,572 (86.5) |
 Yes | 77,671 (4.4) | 22,008 (13.5) |
Decade of first birth | ||
 1973–1979 | 478,412 (26.9) | 39,063 (24.0) |
 1980–1989 | 385,271 (21.6) | 42,506 (26.1) |
 1990–1999 | 386,441 (21.7) | 38,576 (23.7) |
 2000–2012 | 530,674 (29.8) | 42,773 (26.3) |
Parity | ||
 1 | 610,494 (34.3) | 38,564 (23.7) |
 2 | 793,672 (44.6) | 70,936 (43.5) |
 3 | 291,217 (16.4) | 35,819 (22.0) |
 4 | 64,811 (3.6) | 11,970 (7.4) |
 5 or more | 20,604 (1.2) | 5629 (3.5) |