Table 1 Parental socio-demographic characteristics, year of birth and birth characteristics of the studied twins and singletons, by gender
From: Reproductive patterns among twins - a Swedish register study of men and women born 1973-1983
Females | Males | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
Singletons | Twins | Singletons | Twins | |||||||
n | % | n | % | p-value | n | % | n | % | p-value | |
Mother’s educational level | <0.001 | <0.001 | ||||||||
Missing* | 32 269 | 6.6 | 533 | 6.5 | 33 850 | 6.6 | 567 | 6.8 | ||
9-10 years | 139 153 | 28.6 | 2371 | 28.7 | 146 638 | 28.5 | 2331 | 28.0 | ||
11-13 years | 205 252 | 42.2 | 3388 | 41.1 | 216 573 | 42.2 | 3338 | 40.2 | ||
≥14 years | 109 652 | 22.6 | 1956 | 23.7 | 116 740 | 22.7 | 2077 | 25.0 | ||
Father’s educational level | <0.001 | <0.001 | ||||||||
Missing* | 36 483 | 7.5 | 534 | 6.5 | 38 355 | 7.5 | 605 | 7.3 | ||
9-10 years | 153 488 | 31.6 | 2625 | 31.8 | 161 647 | 31.5 | 2567 | 30.9 | ||
11-13 years | 193 682 | 39.8 | 3247 | 39.4 | 204 833 | 39.9 | 3238 | 38.9 | ||
≥14 years | 102 673 | 21.1 | 1842 | 22.3 | 108 966 | 21.2 | 1903 | 22.9 | ||
Mother’s civil status | <0.001 | <0.001 | ||||||||
Divorced/widowed | 16 938 | 3.5 | 349 | 4.2 | 17 752 | 3.5 | 378 | 4.5 | ||
Unmarried | 132 503 | 27.2 | 1960 | 23.8 | 139 369 | 27.1 | 1953 | 23.5 | ||
Married | 336 885 | 69.3 | 5939 | 72.0 | 356 680 | 69.4 | 5982 | 72.0 | ||
Parental country of origin | 0.971 | 0.930 | ||||||||
One or both non-Nordic | 37 553 | 7.7 | 636 | 7.7 | 39 300 | 7.7 | 638 | 7.7 | ||
Both Nordic | 448 773 | 92.3 | 7612 | 92.3 | 474 501 | 92.3 | 7675 | 92.3 | ||
Mother’s age at birth | <0.001 | <0.001 | ||||||||
13-19 years | 27 291 | 5.6 | 284 | 3.4 | 28 543 | 5.6 | 285 | 3.4 | ||
20-26 years | 215 608 | 44.3 | 3137 | 38.0 | 227 765 | 44.3 | 3164 | 38.1 | ||
27-33 years | 194 398 | 40.0 | 3726 | 45.2 | 205 474 | 40.0 | 3748 | 45.1 | ||
≥34 years | 49 029 | 10.1 | 1101 | 13.3 | 52 019 | 10.1 | 1116 | 13.4 | ||
Mother’s parity | <0.001 | <0.001 | ||||||||
Previous children | 278 112 | 57.2 | 5434 | 65.9 | 294 131 | 57.2 | 5659 | 68.1 | ||
No previous children | 208 214 | 42.8 | 2814 | 34.1 | 219 670 | 42.8 | 2654 | 31.9 | ||
Year of birth | <0.001 | <0.001 | ||||||||
Mean/SD | 1977.82/3.18 | 1978.00/3.16 | 1977.82/3.18 | 1978.05/3.19 | ||||||
Size for gestational age | <0.001 | <0.001 | ||||||||
Appropriate for gestational age | 455 865 | 93.7 | 6228 | 75.5 | 481 038 | 93.6 | 6652 | 80.0 | ||
Small for gestational age | 18 573 | 3.8 | 1985 | 24.1 | 18 213 | 3.5 | 1614 | 19.4 | ||
Large for gestational age | 11 888 | 2.4 | 35 | 0.4 | 14 550 | 2.8 | 47 | 0.6 | ||
Birthweight | <0.001 | <0.001 | ||||||||
Normal birthweight (> = 2500 g) | 470 607 | 96.8 | 4860 | 58.9 | 499971 | 97.3 | 5411 | 65.1 | ||
Low birthweight (1500–2499 g) | 14 661 | 3.0 | 3186 | 38.6 | 12840 | 2.5 | 2725 | 32.8 | ||
Very low birthweight (<1500 g) | 1058 | 0.2 | 202 | 2.4 | 990 | 0.2 | 177 | 2.1 | ||
Gestational age | <0.001 | <0.001 | ||||||||
Term (37–42 weeks) | 455 742 | 93.7 | 5406 | 65.5 | 478 279 | 93.1 | 5400 | 65.0 | ||
Preterm (32–36 weeks) | 17 399 | 3.6 | 2548 | 30.9 | 21 909 | 4.3 | 2578 | 31.0 | ||
Very preterm (<32 weeks) | 1539 | 0.3 | 251 | 3.0 | 1779 | 0.3 | 294 | 3.5 | ||
Post term (>42 weeks) | 11 646 | 2.4 | 43 | 0.5 | 11 834 | 2.3 | 41 | 0.5 | ||