| Nonasthmatic | Asthmatic | Total | |
| Subjects | 166 517 | 11 512 | 178 029 |
| Pre-existing hypertension | 2022 (1.2) | 218 (1.9) | 2240 (1.3) |
| Nonsmoker | 1712 (1.3) | 166 (2.0) | 1878 (1.3) |
| Smoker | 310 (1.1) | 52 (1.8) | 362 (1.1) |
| Pre-existing diabetes | 825 (0.5) | 99 (0.9) | 924 (0.5) |
| Nonsmoker | 647 (0.5) | 60 (0.7) | 707 (0.5) |
| Smoker | 178 (0.6) | 39 (1.4) | 217 (0.7) |
| Hypertensive disorders of pregnancy | 11 958 (7.2) | 1118 (9.7) | 13 076 (7.3) |
| Nonsmoker | 10 363 (7.8) | 906 (10.9) | 11 269 (8.0) |
| Smoker | 1595 (5.7) | 212 (7.5) | 1807 (5.9) |
| Gestational diabetes | 6354 (3.8) | 544 (4.7) | 6868 (3.9) |
| Nonsmoker | 5393 (4.0) | 409 (4.9) | 5802 (4.1) |
| Smoker | 961 (3.4) | 135 (4.8) | 1096 (3.6) |
| Antepartum haemorrhage | |||
| Abruption | 1013 (0.69) | 105 (0.9) | 1118 (0.6) |
| Nonsmoker | 731 (0.5) | 56 (0.7) | 787 (0.6) |
| Smoker | 282 (1.0) | 49 (1.7) | 331 (1.1) |
| Placenta praevia | 944 (0.6) | 75 (0.7) | 1019 (0.6) |
| Nonsmoker | 746 (0.6) | 53 (0.6) | 799 (0.6) |
| Smoker | 198 (0.7) | 22 (0.8) | 220 (0.7) |
| Unknown cause | 3814 (2.2) | 356 (3.1) | 4170 (2.3) |
| Nonsmoker | 2927 (2.2) | 238 (2.9) | 3165 (2.2) |
| Smoker | 887 (3.2) | 118 (4.2) | 1005 (3.3) |
| Urinary tract infection | 3897 (2.3) | 443 (3.8) | 4340 (2.4) |
| Nonsmoker | 2794 (2.1) | 294 (3.5) | 3088 (2.2) |
| Smoker | 1103 (4.0) | 149 (5.3) | 1252 (4.1) |
| Polyhydramnios | 721 (0.4) | 76 (0.7) | 797 (0.4) |
| Nonsmoker | 549 (0.4) | 51 (0.6) | 600 (0.4) |
| Smoker | 172 (0.6) | 25 (0.9) | 197 (0.6) |
| Elective Caesarean | 21 099 (12.7) | 1548 (13.4) | 22 647 (12.7) |
| Nonsmoker | 18 128 (15.6) | 1213 (16.9) | 19 341 (13.7) |
| Smoker | 2971 (11.7) | 335 (12.9) | 3306 (10.8) |
| Emergency Caesarean | 25 642 (15.4) | 2056 (17.9) | 27 698 (15.6) |
| Nonsmoker | 21 662 (18.7) | 1577 (21.9) | 23 239 (16.4) |
| Smoker | 3980 (15.7) | 479 (18.5) | 4459 (14.5) |
| Premature labour | 5223 (3.1) | 428 (3.7) | 5651 (3.2) |
| Nonsmoker | 3825 (2.9) | 249 (3.0) | 4074 (2.9) |
| Smoker | 1398 (5.0) | 179 (6.3) | 1577 (5.1) |
| PROM | 3201 (1.9) | 275 (2.4) | 3476 (2.0) |
| Nonsmoker | 2372 (1.8) | 173 (2.1) | 2545 (1.8) |
| Smoker | 829 (3.0) | 102 (3.6) | 931 (3.0) |
| Isoimmunisation | 468 (0.3) | 30 (0.3) | 498 (0.3) |
| Nonsmoker | 364 (0.3) | 22 (0.3) | 386 (0.3) |
| Smoker | 104 (0.4) | 8 (0.3) | 112 (0.4) |
| Last pregnancy stillbirth | 608 (0.4) | 52 (0.5) | 660 (0.3) |
| Nonsmoker | 480 (0.5) | 34 (0.6) | 514 (0.4) |
| Smoker | 128 (0.6) | 18 (0.8) | 146 (0.5) |
Data are presented as n or n (%). PROM: premature rupture of membranes.