TABLE 3.
Adjusted relative risks (RRs) and 95% confidence intervals (CIs) of endometriosis risk by rotating night shift work in three categories among premenopausal women in the Nurses’ Health Study II (1989–2003), excluding permanent night workers.
| Never infertility work-up | Ever infertility work-up | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| Duration of rotating night shift |
Cases | Person years |
Age- adjusted RRb |
MV RR (95% CI)c |
Cases | Person years |
Age- adjusted RRb |
MV RR (95% CI)c |
Pc |
| Baseline exposure | |||||||||
| Never | 477 | 288,011 | 1.00 | 1.00 | 344 | 47,785 | 1.00 | 1.00 | 0.13 |
| 1–4.9 years | 514 | 324,807 | 0.95 (0.84, 1.08) | 0.96 (0.85, 1.09) | 427 | 58,234 | 1.00 (0.86, 1.15) | 0.95 (0.82,1.10) | |
| ≥5 years | 103 | 72,056 | 0.84 (0.68, 1.04) | 0.80 (0.64, 0.99) | 107 | 14,198 | 1.16 (0.93, 1.44) | 1.07 (0.85, 1.34) | |
| P for trend | 0.07 | 0.89 | |||||||
| Cumulative update | |||||||||
| Never | 423 | 254,712 | 1.00 | 1.00 | 308 | 42,575 | 1.00 | 1.00 | 0.21 |
| 1–4.9 years | 531 | 333,346 | 0.97 (0.86, 1.11) | 0.97 (0.86, 1.11) | 432 | 58,726 | 1.02 (0.87, 1.18) | 0.96 (0.82, 1.11) | |
| ≥5 years | 140 | 96,816 | 0.90 (0.74, 1.09) | 0.86 (0.70, 1.04) | 138 | 18,917 | 1.18 (0.96, 1.45) | 1.10 (0.89, 1.36) | |
| P for trend | 0.16 | 0.60 | |||||||
Note: RR=rate ratio; MV=multivariate; CI=confidence interval
Adjusted for current age (continuous months) and calendar time (2-year questionnaire period).
Adjusted for current age (continuous months), calendar time (2-year questionnaire period), age at menarche (<10, 10, 11, 12, 13, 14, 15, >15), menstrual cycle regularity (very regular, regular, usually regular, always regular, no periods) between ages 18–22, parity (nulliparous, 1, 2, 3, ≥4), oral contraceptive use (never, past, current), body mass index (<19, 19–20.4, 20.5–21.9, 22.0–24.9, 25.0–29.9, ≥30), alcohol consumption (nondrinkers, <5 g/day, 5–9.9 g/day, ≥10 g/day), smoking status (never, former, current), and physical activity (<3, 3–8.9, 9–17.9, 18–26.9, 27–41.9, ≥42 MET-hr/week).
P value, test for heterogeneity comparing the effect of rotating nightshift work among women who have never reported having had a clinical evaluation for infertility with those who have ever reported having had a clinical infertility evaluation.