Characteristics of the study population according to exposure of night work (n=22 744)
| Characteristics | Exposed ≥1 registered night shift during pregnancy week 3–21 (n=10 047) | Reference group No registered night shifts during pregnancy week 3–21 (n=12 697) |
| Outcome of pregnancy, n (%) | ||
| Births | 9 089 (90) | 11 007 (87) |
| Miscarriages | 740 (8) | 1 149 (9) |
| Molar and ectopic pregnancies | 44 | 96 (1) |
| Induced abortions | 174 (2) | 445 (3) |
| Time for miscarriage (pregnancy week) | ||
| Gestational age, median (min, max) | 9.0 (4.0, 21.0) | 8.0 (4.0, 21.0) |
| Follow-up weeks at risk, median (Pct 25, 75) | 22 (22,22) | 22 (22,22) |
| Work during pregnancy weeks 3–21, median (Pct 25,75) | ||
| Number of day shifts | 40 (25, 52) | 50 (11, 80) |
| Number of evening shifts | 6 (0, 16) | 0 (0, 2) |
| Number of night shifts | 9 (4,16) | |
| Maternal age at conception | ||
| Mean years (SD) | 30.5 (3.9) | 30.9 (4.4) |
| ≤25 years, n (%) | 512 (5) | 1 028 (8) |
| 26–30 years, n (%) | 4 531 (45) | 4 701 (37) |
| >30 years, n (%) | 5 004 (50) | 6 968 (55) |
| Parity, n (%) | ||
| 0 | 5 948 (59) | 6 967 (55) |
| 1 | 2 442 (24) | 3 434 (27) |
| 2+ | 1 411 (14) | 1 963 (15) |
| Missing | 246 (2) | 333 (3) |
| Former miscarriage, yes n (%) | 736 (7) | 1 104 (9) |
| BMI before pregnancy Mean (SD) | 23.7 (4.3) | 23.9 (4.6) |
| Underweight (<18.5 kg/m2), n (%) | 743 (7) | 977(8) |
| Normal weight (18.5–24.9 kg/m2), n (%) | 6 646 (66) | 8 167 (64) |
| Overweight (25.0–29.9 kg/m2), n (%) | 1 818 (18) | 2 382 (19) |
| Obese (30+kg/m2), n (%) | 840 (8) | 1 171 (9) |
| Smoking during pregnancy, n (%) | ||
| Non-smoker | 9 252 (92) | 11 579 (91) |
| Smoker | 492 (5) | 726 (6) |
| Missing | 303 (3) | 392 (3) |
| Socio-economic status (SES), n (%) | ||
| Low | 869 (9) | 3 563 (28) |
| Medium | 6 939 (69) | 6 811 (53) |
| High | 2 224 (22) | 2 230 (18) |
| Missing | 15 | 93 (1) |
| Most frequent occupation, n (%)* | ||
| Nurse | 6 242 (62) | 3 405 (27) |
| Physician | 1 732 (17) | 955 (8) |
| Medical secretary | 53 | 1 373 (11) |
| Physiotherapist/occupational therapist | 29 | 1 175 (10) |
| Nurse assistant | 510 (5) | 727 (6) |
| Laboratory technician | 233 (2) | 642 (5) |
| Cleaning/kitchen worker | 17 | 557 (4) |
| Pedagogue/care helper | 230 (2) | 383 (3) |
| Psychologist | <10 | 418 (3) |
| Midwife | 305 (3) | 41 |
| Office worker | 10 | 304 (2) |
| Teacher/scientist | 81 (1) | 300 (2) |
*Among occupations with at least 100 employees.