Table 3.
Associations between occupational factors and risk of miscarriage among 1074 firefighters and 1864 pregnanciesa,b
| Miscarriages N (%) |
RR (95% CI) Model 1c |
RR (95% CI) Model 2d |
||
|---|---|---|---|---|
| Firefighter subgroups | ||||
| Employment, stratified by wildland firefighter status | ||||
| Structural | No | Yes | ||
| Career | 891 (76%) | 281 (24%) | 1.00 (Ref.) | 1.00 (Ref.) |
| Volunteer | 140 (69%) | 64 (31%) | 1.41 (1.11–1.79) | 1.42 (1.11–1.80) |
| Wildland/WUI | No | Yes | ||
| Career | 388 (90%) | 41 (10%) | 1.00 (Ref.) | 1.00 (Ref.) |
| Volunteer | 38 (68%) | 18 (32%) | 3.09 (1.76–5.42) | 2.53 (1.35–4.78) |
| Interaction p-value e | < 0.01 | < 0.01 | ||
| Work practices | ||||
| Shift schedule of career firefighters, stratified by age at pregnancy | ||||
| < 35 years old | No | Yes | ||
| Less than 24 h on shift | 232 (77%) | 69 (23%) | 1.00 (Ref.) | 1.00 (Ref.) |
| 24 or more hr. on shift | 772 (84%) | 144 (16%) | 0.67 (0.50–0.90) | 0.74 (0.55–0.99) |
| 35+ years old | No | Yes | ||
| Less than 24 h on shift | 64 (78%) | 18 (22%) | 1.00 (Ref.) | 1.00 (Ref.) |
| 24 or more hr. on shift | 211 (70%) | 89 (30%) | 1.29 (0.84–2.00) | 1.28 (0.82–1.99) |
| Interaction p-value f | 0.01 | 0.02 | ||
| Worked fire/rescue calls at pregnancy start | No | Yes | ||
| No | 138 (70%) | 58 (30%) | 1.00 (Ref.) | 1.00 (Ref.) |
| Yes | 1250 (79%) | 340 (21%) | 0.81 (0.60–1.09) | 0.82 (0.61–1.11) |
RR Relative risk, CI confidence interval, BMI Body mass index (kg/m2), WUI wildland urban interface
a Generalized estimating equations models with Poisson distribution and sandwich variance estimators were used to estimate risk ratios and 95% CIs
b 86 pregnancies had missing information for wildland status (3), shift schedule (5) and fire/rescue calls (78) and were not included in those models
c Model 1 is adjusted for age at pregnancy, modeled as age at pregnancy and (age at pregnancy)2
d 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
e p-value for interaction between employment and wildland firefighter status
f p-value for interaction between shift schedule and age at pregnancy, among career firefighters