Characteristics of women who used assisted conception and their children, Denmark 1995–2003
| Natural conception | Assisted conception | p Value | IVF | OI | p Value | |
| Maternal age | <0.001 | <0.001 | ||||
| 20–24 | 81 371 (14.6) | 1175 (3.6) | 206 (1.4) | 969 (5.39) | ||
| 25–29 | 211 078 (38.0) | 8423 (25.4) | 2822 (18.8) | 5601 (30.9) | ||
| 30–34 | 186 934 (33.6) | 14185 (42.8) | 6791 (45.3) | 7394 (40.7) | ||
| 35–39 | 66 776 (12.0) | 8174 (24.7) | 4547 (30.3) | 3627 (20.0) | ||
| 40+ | 9651 (1.8) | 1182 (3.5) | 625 (4.2) | 557 (3.1) | ||
| Parity | <0.001 | <0.001 | ||||
| Primiparous | 228 059 (41.0) | 22171 (66.9) | 11099 (74.0) | 11072 (61.0) | ||
| Multiparous | 327 746 (58.9) | 10968 (33.1) | 3892 (26.0) | 7076 (39.0) | ||
| Educational level (years) | <0.001 | 0.002 | ||||
| Lower (9–10) | 111 404 (23.1) | 4641 (16.7) | 2175 (17.5) | 2466 (16.1) | ||
| Intermediate (11–16) | 331 842 (68.7) | 20187 (72.7) | 8975 (72.3) | 11212 (73.1) | ||
| Higher (17+) | 39 663 (8.2) | 2930 (10.6) | 1261 (10.2) | 1669 (10.8) | ||
| Smoking | <0.001 | <0.001 | ||||
| Non-smoker | 429 728 (77.7) | 26 670 (83.7) | 12 293 (82.4) | 15 377 (84.8) | ||
| Smoker or stopped in pregnancy | 123 512 (22.3) | 5386 (16.3) | 2631 (17.6) | 2755 (15.2) | ||
| Multiplicity | <0.001 | <0.001 | ||||
| Singletons | 541 616 (97.6) | 23 483 (70.9) | 8501 (56.7) | 14 982 (82.6) | ||
| Twins | 13 376 (2.4) | 9120 (27.5) | 6234 (41.6) | 2886 (15.9) | ||
| Triplets | 215 (0.0) | 495 (1.5) | 239 (1.6) | 256 (1.4) | ||
| Quadruplets | 4 (0.0) | 17 (0.1) | 5 (0.1) | 12 (0.1) | ||
| Gestational age (weeks) | <0.001 | <0.001 | ||||
| 20–27 | 1247 (0.2) | 397 (1.2) | 278 (1.9) | 119 (0.7) | ||
| 28–31 | 3275 (0.6) | 868 (2.6) | 529 (3.6) | 339 (1.9) | ||
| 32–36 | 26 319 (4.8) | 5177 (15.7) | 3108 (20.8) | 2069 (11.4) | ||
| 37–41 | 474 346 (85.9) | 24 882 (75.3) | 10 613 (71.2) | 14 269 (78.6) | ||
| 42+ | 46 745 (8.5) | 1728 (5.2) | 377 (2.5) | 1351 (7.4) | ||
| Birth weight (g) | <0.001 | <0.001 | ||||
| 500–1499 | 3864 (0.7) | 1116 (3.4) | 672 (4.6) | 444 (2.5) | ||
| 1500–2499 | 19 930 (3.6) | 4680 (14.3) | 2864 (19.4) | 1816 (10.1) | ||
| 2500+ | 527 278 (95.7) | 29 957 (82.3) | 11 214 (76.0) | 15 743 (87.4) | ||
Data shown as numbers (percentages). Natural conception compared with the combined assisted conception group and in vitro fertilisation (IVF) compared with ovulation induction (OI).