Age-standardised prevalence ratios comparing preterm births among most recent live birth of firefighters with non-firefighting US populations
| Observed events | Expected events | aSPR (95% CI) | |
| Compared with US birth certificates* | |||
| All firefighters (n=945) | 131 | 92.8 | 1.41 (1.18 to 1.68) |
| Employment status | |||
| Career (n=828) | 104 | 81.0 | 1.28 (1.05 to 1.56) |
| Volunteer (n=117) | 27 | 11.8 | 2.29 (1.51 to 3.34) |
| Wildland firefighter status | |||
| Wildland/combination (n=333) | 23 | 32.9 | 0.72 (0.46 to 1.08) |
| Structural (n=610) | 107 | 60.6 | 1.77 (1.45 to 2.13) |
| Compared with US nurses from the Nurses’ Health Study II† | |||
| All firefighters (N=934) | 120 | 76.5 | 1.57 (1.30 to 1.88) |
| Employment status | |||
| Career (n=818) | 94 | 67.0 | 1.40 (1.13 to 1.72) |
| Volunteer (n=116) | 26 | 9.5 | 2.75 (1.80 to 4.03) |
| Wildland firefighter status | |||
| Wildland/combination (n=331) | 22 | 26.8 | 0.82 (0.51 to 1.24) |
| Structural (n=601) | 97 | 49.5 | 1.96 (1.59 to 2.90) |
Combination= does wildland firefighting in addition to working for a career or volunteer department.
*Martin et al 16 (https://www.cdc.gov/nchs/data/nvsr/nvsr68/nvsr68_13-508.pdf) included 3 791 712 births (including multiple gestations) to women in the USA collected from registered birth certificates in 2018.
†Lawson et al 15 (https://pubmed.ncbi.nlm.nih.gov/18976732/) included 6977 women from the Nurses’ Health Study II who self-reported details about their most recent singleton live birth pregnancy while working as a nurse between 1993 and 2000.
aSPR, age-at-pregnancy standardised prevalence ratio.