Association between physical labour at work in the past month and duration of ongoing pregnancy attempt in Nurses’ Health Study 3 women (n=1739)
| N (%) | Median duration in months (25th, 75th percentile) | Model 1 time ratio (95% CI) | Model 2 time ratio (95% CI) | Model 3 time ratio (95% CI) | |
|---|---|---|---|---|---|
| Duration of standing/walking (h/day) | |||||
| 0 or less than 1 | 114 (6.6) | 4.0 (1, 12) | 1.07 (0.86 to 1.33) | 1.05 (0.85 to 1.30) | 1.19 (0.95 to 1.49) |
| 1–4 | 438 (25.3) | 4.0 (1, 11) | 0.94 (0.82 to 1.08) | 0.94 (0.82 to 1.07) | 0.99 (0.86 to 1.14) |
| 5–8 | 583 (33.7) | 3.0 (1, 10) | 1.0 (REF) | 1.0 (REF) | 1.0 (REF) |
| >8 | 595 (34.4) | 3.0 (1, 10) | 1.01 (0.90 to 1.15) | 1.02 (0.90 to 1.15) | 0.98 (0.86 to 1.11) |
| P-trend | 0.60 | 0.46 | 0.39 | ||
| Frequency of moving or lifting a heavy load (25+ lbs) (times/day) | |||||
| None | 536 (30.9) | 3.0 (1, 9) | 1.0 (REF) | 1.0 (REF) | 1.0 (REF) |
| 1–5 | 696 (40.2) | 3.0 (1, 11) | 1.13 (1.00 to 1.28) | 1.12 (1.00 to 1.27) | 1.13 (1.00 to 1.28) |
| 6–15 | 383 (22.1) | 3.0 (1, 9) | 1.16 (1.00 to 1.33) | 1.14 (0.99 to 1.32) | 1.15 (0.99 to 1.33) |
| >15 | 117 (6.8) | 5.0 (2, 12) | 1.56 (1.25 to 1.94) | 1.50 (1.21 to 1.85) | 1.49 (1.20 to 1.85) |
| P-trend | 0.0005 | 0.001 | 0.002 |
Accelerated failure time models were used to estimate the time ratios and 95% CIs. Tests for linear trend use the median values in each category as a continuous variable.
Model 1 is adjusted for age.
Model 2 is adjusted for age, race, BMI, smoking status and marital status.
Model 3 is adjusted for variables in Model 2 and current night work, weekly hours of nursing work, duration of night work, and current exposure to radiation, antineoplastic drugs, high-level disinfectants, and anaesthesia gas. Model 3 for duration of standing/walking was also further adjusted for frequency of moving or lifting a heavy load.
BMI, body mass index.