Associations between pregnancy-specific occupational factors and risk of preterm birth among 934 firefighters and 1356 pregnancies*†
| Preterm births n (%) | RR (95% CI) Model 1‡ | RR (95% CI) Model 2§ | RR (95% CI) Model 3¶ | ||
| Fire responses during pregnancy | |||||
| Worked fire/rescue calls at pregnancy start | No | Yes | |||
| No | 119 (89%) | 14 (11%) | 1.00 (Ref.) | 1.00 (Ref.) | 1.00 Ref.) |
| Yes | 1071 (88%) | 146 (12%) | 1.19 (0.71–2.00) | 1.21 (0.73–2.02) | 1.20 (0.72–2.00) |
| No of fires responded to during pregnancy | No | Yes | |||
| 0 fires | 309 (87%) | 46 (13%) | 1.00 (Ref.) | 1.00 (Ref.) | 1.00 (Ref.) |
| 1–4 fires | 470 (87%) | 73 (13%) | 1.13 (0.79–1.63) | 1.11 (0.77–1.60) | 1.15 (0.80–1.65) |
| ≥5 fires | 383 (92%) | 34 (8%) | 0.71 (0.45–1.10) | 0.83 (0.53–1.29) | 0.83 (0.54–1.29) |
| Work restriction during pregnancy | |||||
| Was work restricted during pregnancy? | No | Yes | |||
| No | 261 (87%) | 39 (13%) | 1.00 (Ref.) | 1.00 (Ref.) | 1.00 (Ref.) |
| Yes | 918 (89%) | 115 (11%) | 0.87 (0.60–1.25) | 0.95 (0.65–1.38) | 1.00 (0.68–1.46) |
| Timing of start of work restriction | No | Yes | |||
| None/during 3rd trimester | 317 (86%) | 51 (14%) | 1.00 (Ref.) | 1.00 (Ref.) | 1.00 (Ref.) |
| 2nd trimester | 502 (92%) | 41 (8%) | 0.57 (0.37–0.86) | 0.64 (0.42–0.98) | 0.67 (0.43–1.03) |
| 1st trimester | 351 (86%) | 59 (14%) | 1.06 (0.73–1.55) | 1.09 (0.75–1.59) | 1.13 (0.77–1.64) |
*Generalised estimating equations with Poisson distribution and sandwich variance estimators were used to estimate relative risks and 95% CIs.
†A total of 102 total pregnancies had missing information for worked fire/rescue calls (6), number of fires (40), work restriction (23) and time of work restriction (35) and were not included in those models.
‡Model 1 is adjusted for age-at-pregnancy, modelled as age-at-pregnancy and age-at-pregnancy.2
§Model 2 is additionally adjusted for highest education completed (some college/at least college degree), gravidity (yes/no), BMI (<30 kg/m2/≥30 kg/m2) and smoking status (current or former/never). Highest education completed, BMI and smoking status were measured in 2017 at time of survey. Gravidity was assessed for each pregnancy.
¶Model 3 is additionally adjusted for employment status (career/volunteer).
BMI, body mass index; RR, relative risk.