TABLE 4.
Association of Age, Parity, Physical Job Demands, Absorbed Dose, and Standard Sleep Interval Time (Analyzed Simultaneously) with Early Miscarriage (Gestational Weeks 4–13) According to Time Perioda
| Weeks 4–8 |
Weeks 9–13 |
Weeks 4–13 |
|||||||
|---|---|---|---|---|---|---|---|---|---|
| Variableb | No. Pregnancies | No. Miscarriages | OR (95% CI) | No. Pregnancies | No. Miscarriages | OR (95% CI) | No. Pregnancies | No. Miscarriages | OR (95% CI) |
| Model 1 | Model 2 | Model 3 | |||||||
| Age at last menstrual period (1 year) | 797 | 78 | 1.1 (1.1–1.2) | 719 | 69 | 1.0 (0.96–1.1) | 797 | 147 | 1.1 (1.0–1.1) |
| Parity | |||||||||
| Nulliparousc | 478 | 45 | 1.0 | 433 | 47 | 1.0 | 478 | 92 | 1.0 |
| Parous | 319 | 33 | 0.91 (0.56–1.5) | 286 | 22 | 0.70 (0.43–1.2) | 319 | 55 | 0.81 (0.57–1.2) |
| Physical job demands in pregnancyd | |||||||||
| Lowc | 157 | 8 | 1.0 | 149 | 6 | 1.0 | 157 | 14 | 1.0 |
| High | 640 | 70 | 2.2 (1.1–4.5) | 570 | 63 | 2.8 (1.2–6.4) | 640 | 133 | 2.5 (1.5–4.1) |
| Absorbed dose and Standard Sleep Interval travele | |||||||||
| No work flightsf | 75 | 15 | 2.6 (1.4–4.9) | 60 | 5 | 1.6 (0.54–4.6) | 75 | 20 | 2.3 (1.3–4.0) |
| Low–low (<0.1 mGy and <15 hours)c | 164 | 28 | 1.0 | 136 | 9 | 1.0 | 164 | 37 | 1.0 |
| Low–high (<0.1 mGy and ≥15 hours) | 27 | 8 | 1.8 (0.86–3.9) | 19 | 3 | 2.4 (0.64–9.3) | 27 | 11 | 2.0 (1.0–3.9) |
| High–low (≥0.1 mGy and <15 hours) | 178 | 11 | 1.2 (0.55–2.4) | 167 | 15 | 1.5 (0.69–3.4) | 178 | 26 | 1.3 (0.76–2.1) |
| High–high (≥0.1 mGy and ≥15 hours) | 353 | 16 | 0.97 (0.50–1.9) | 337 | 37 | 2.3 (1.1–4.6) | 353 | 53 | 1.6 (1.0–2.5) |
Models of pregnancies in weeks 4–13 included 797 flight attendant study pregnancies (11 miscarriages in gestational weeks 1–3 and 32 pregnancies with 1 or more missing covariates were excluded).
All variables were included in each model; however, estimates for age and parity are not necessarily interpretable as total effects.24
Reference category.
High physical job demands defined as (1) being on your feet (including standing and walking) more than 8 hours/day or (2) 2 or more of the following: lifting or carrying objects that weigh at least 15 pounds more than 10 times a day, bending at the waist more than 25 times/day, and pushing or pulling heavy objects requiring at least 15 pounds of force or effort 20 or more times/day.
Cumulative occupational exposure metrics were evaluated from the estimated date of last menstrual period through the cutoff week; cutpoints reflect the median exposure among cases.
Some employed flight attendants did not incur work flights during the first trimester.