Descriptive statistics
| Participants, n | Preterm birth, % | SGA, % | Pregnancy-induced hypertensive disorders, % | First trimester average NOx levels, µg/m3 (SD) | Annual daily average traffic (year of birth), vehicles/day (SD) | |
|---|---|---|---|---|---|---|
| Maternal asthma | ||||||
| Yes | 17 981 | 3.1 | 9.8 | 3.1 | 14.9 (7.2) | 3536 (7767) |
| No | 84 787 | 2.7 | 9.8 | 2.6 | 15.1 (7.4) | 3576 (7700) |
| Maternal level of education | ||||||
| Pre-upper secondary school (9 years) | 9841 | 3.4 | 13 | 2.1 | 12.7 (5.7) | 2516 (6550) |
| Upper secondary school (2 years) | 34 755 | 3.0 | 10 | 2.9 | 14.3 (7.0) | 3248 (7489) |
| Post-upper secondary school (<3 years) | 16 578 | 2.4 | 8.8 | 2.9 | 15.6 (7.7) | 3800 (7978) |
| Post-secondary school (3 years) | 38 763 | 2.7 | 9.0 | 2.6 | 16.1 (7.7) | 4032 (8066) |
| Postgraduate education | 1898 | 2.7 | 8.8 | 2.1 | 16.5 (7.8) | 3697 (7107) |
| Parity | ||||||
| 1 | 42 870 | 2.9 | 11 | 2.9 | 15.4 (7.5) | 3714 (7975) |
| 2 | 38 290 | 2.8 | 9.6 | 2.6 | 15.0 (7.4) | 3502 (7483) |
| 3 | 16 225 | 2.4 | 8.4 | 2.3 | 14.6 (7.2) | 3401 (7582) |
| 4 or more | 5383 | 2.5 | 9.0 | 2.6 | 14.6 (7.0) | 3390 (7544) |
| Maternal origin | ||||||
| Africa | 6815 | 2.2 | 15 | 1.7 | 11.7 (4.2) | 1888 (5140) |
| USA | 2644 | 3.6 | 9.5 | 2.5 | 14.5 (7.1) | 3135 (7004) |
| Asia and Oceania | 5391 | 3.6 | 16 | 1.9 | 13.6 (6.5) | 2817 (6538) |
| Europe | 4376 | 2.6 | 11 | 1.6 | 14.4 (7) | 3274 (7098) |
| Middle East | 5806 | 3.1 | 15 | 1.7 | 11.7 (4.8) | 2141 (6099) |
| Nordic | 77 334 | 2.7 | 8.5 | 3.0 | 15.8 (7.7) | 3911 (8100) |
| Maternal smoking | ||||||
| Non-smoker | 82 565 | 2.6 | 9.6 | 2.7 | 14.9 (7.2) | 3490 (7659) |
| Moderate smoker | 4064 | 3.3 | 15 | 1.6 | 13.8 (6.5) | 3098 (6960) |
| Heavy smoker | 1540 | 3.3 | 19 | 1.8 | 13.1 (5.8) | 2719 (7476) |
| Maternal pre-pregnancy BMI | ||||||
| Underweight | 2363 | 2.9 | 18 | 1.1 | 15.4 (7.6) | 3809 (7844) |
| Normal weight | 56 268 | 2.6 | 10 | 2.1 | 15.3 (7.3) | 3683 (7828) |
| Overweight | 16 592 | 2.4 | 8.4 | 3.5 | 13.8 (6.6) | 2950 (7120) |
| Obesity | 5664 | 2.7 | 8.7 | 5.8 | 12.9 (5.9) | 2609 (6390) |
| Family situation | ||||||
| Cohabiting | 84 307 | 2.6 | 9.7 | 2.6 | 14.9 (7.2) | 3478 (7660) |
| Living alone | 2250 | 2.6 | 13 | 2.2 | 13.5 (5.9) | 2652 (6162) |
| Other | 2664 | 3.5 | 14 | 2.9 | 14.2 (6.7) | 3247 (7306) |
BMI, body mass index; NOx, nitrogen oxides; SGA, small for gestational age.