Weekly working hours, shift work, standing and risk of preterm delivery
| First author (year) | Numbers in analysis | RR (95% CI) | Exposure | Higher potential for | Incomplete reporting | Pooled in meta-analysis | ||
|---|---|---|---|---|---|---|---|---|
| Comparison | Timing | Bias | Confounding | |||||
| h/d, hours per day; h/wk, hours per week. | ||||||||
| RR is used generically to encompass a variety of published effect measures (odds ratios, incidence density ratios, hazard ratios and so on). | ||||||||
| *Excluded from sensitivity analysis. | ||||||||
| †Effective response rate <50%. | ||||||||
| ‡Not pooled as a standard error could not be derived from the published data. | ||||||||
| §Second trimester chosen for meta-analysis (being the most comparable with other studies). | ||||||||
| Weekly working hours | ||||||||
| Cohort studies | ||||||||
| Brink-Henriksen T (1995)10 | 927 | 1.87 (0.78 to 4.16) | ⩾45 vs <30 h/wk | 16 weeks | No | No | No | Yes |
| Hickey CA (1995)17 | 183 | 0.68 (0.12 to 2.7) | >40 vs 1–20 h/wk | 24–26 weeks | No | No | Yes | Yes* |
| Pompeii LA (2005)38 | 1037 | 0.6 (0.4 to 0.9) | >46 vs 35–45 h/wk | Trimester 1 | No | No | No | No |
| Pompeii LA (2005)38 | 1037 | 0.4 (0.2 to 0.8) | >46 vs 35–45 h/wk | Trimester 2 | No | No | No | No |
| Pompeii LA (2005)38 | 1037 | 0.3 (0.1 to 0.7) | >46 vs 35–45 h/wk | Trimester 3 | No | No | No | No |
| Tuntiseranee P (1998)52 | 886 | 1.6 (0.8 to 3.3) | ⩾61 vs ⩽50 h/wk | 15–28 weeks | No | No | No | No |
| Case–control studies | ||||||||
| Luke B† (1995)24 | 1470 | 1.6 (1.1 to 2.2) | >36 vs ⩽36 h/wk | Not stated | No | No | No | No |
| Saurel-Cubizolles MJ (2004)45 | 2062 | 1.33 (1.1 to 1.6) | ⩾43 vs 30–39 h/wk | Trimester 1 | No | No | Yes | Yes* |
| Cross-sectional studies | ||||||||
| Bodin L (1999)8 | 1685 | 1.3 (0.6 to 2.7) | ⩾36 vs 21–35 h/wk | Trimester 2 | No | No | No | No |
| Ceron-Mireles P (1996)11 | 2429 | 1.21 (0.9 to 1.62) | >50 vs 3–25 h/wk | Not stated | No | No | No | Yes |
| Fortier I (1995)13 | 1833 | 1.14 (0.71 to 1.82) | ⩾40 vs <30 h/wk | Not stated | No | No | No | Yes |
| Klebanoff MA (1990)20 | 989 | 1.2 (0.8 to 1.7) | Residents (>100 h) vs others | Any | No | No | No | No |
| Mamelle N (1984)27 | 1928 | 1.7 (1.1 to 2.5) | >41 vs ⩽40 h/wk | Not stated | No | Yes | Yes | Yes* |
| McDonald AD (1988)29 | 22761 | 1.34, p<0.05 | ⩾46 vs <46 h/wk | Not stated | No | No | No | No‡ |
| Peoples-Sheps MD (1991)36 | 1853 | 1.1 (0.7 to 1.8) | ⩾40 vs 1–20 h/wk | Not stated | No | No | No | Yes |
| Saurel-Cubizolles MJ (1987)43 | 2245 | 0.59 (0.21 to 1.37) | ⩾42 vs <42 h/wk | Trimester 1 | No | Yes | Yes | No |
| Saurel-Cubizolles MJ (1991)44 | 873 | 1.0 (0.4 to 2.5) | >45 vs ⩽45 h/wk | Not stated | No | No | Yes | No |
| Savitz DA (1996)46 | 1015 | 1.1 (0.8 to 1.5) | ⩾40 vs no paid work | 5 months | No | No | No | Yes |
| Shift work | ||||||||
| Cohort studies | ||||||||
| Misra DP (1998)32 | 1166 | 1.0 (0.59 to 1.69) | Shifts vs none | Trimesters 1 and 2 | No | No | No | Yes |
| Pompeii LA (2005)38 | 1796 | 1.5 (1.0 to 2.1) | Regular night work (yes vs no) | Trimester 1 | No | No | No | — |
| Pompeii LA (2005)38 | 1796 | 1.6 (1.0 to 2.8) | Regular night work (yes vs no) | Trimester 2 | No | No | No | Yes§ |
| Pompeii LA (2005)38 | 1796 | 1.8 (0.8 to 3.4) | Regular night work (yes vs no) | Trimester 3 | No | No | No | — |
| Stinson JC† (2003)49 | 359 | 1.8 (0.93 to 3.53) | Night vs day | 22–26 weeks | No | No | No | Yes |
| Xu X (1994)55 | 887 | 2.0 (1.1 to 3.4) | Rotating shift work (yes vs no) | Not stated | No | No | No | Yes |
| Zhu JL (2004)56 | 35662 | 0.97 (0.8 to 1.17) | Rotating shift work vs daytime work | Trimesters 1 and 2 | No | No | No | Yes |
| Case–control studies | ||||||||
| Hartikainen-Sorri AL (1989)15 | 358 | 0.86 (0.51 to 1.45) | Shift work (yes vs no) | Not stated | No | Yes | Yes | Yes* |
| Luke B† (1995)24 | 1470 | 1.5 (1.1 to 2.1) | Evening/night vs day | Not stated | Yes | No | No | Yes* |
| Saurel-Cubizolles MJ (2004)45 | 6309 | 0.97 (0.8 to 1.1) | Shift work (yes vs no) | Trimester 1 | No | No | Yes | Yes |
| Cross-sectional studies | ||||||||
| Bodin L (1999)8 | 1685 | 5.6 (1.9 to 16.4) | Night vs day | Trimester 2 | No | No | No | Yes |
| Fortier I (1995)13 | 4118 | 1.03 (0.72 to 1.48) | Shift work vs day only | Not stated | No | No | No | Yes |
| Mamelle N (1984)27 | 1928 | 1.6 (1.0 to 2.5) | Shift and night work vs none | Not stated | No | Yes | Yes | Yes* |
| McDonald AD (1988)29 | 22761 | 1.18, p>0.05 | Changing shift vs not | Not stated | No | No | No | No‡ |
| Nurminen T (1989)34 | Unclear | 0.9 (0.7 to 1.1) | Shift work (yes vs no) | Not stated | No | No | No | Yes |
| Saurel-Cubizolles MJ (1987)43 | 2261 | 0.8 (0.16 to 2.51) | Night vs day | Trimester 1 | No | Yes | Yes | Yes* |
| Standing | ||||||||
| Cohort studies | ||||||||
| Brink-Henriksen T (1995)10 | 4259 | 1.2 (0.6 to 2.4) | >5 vs 0–2 h/d | 16 weeks | No | No | No | Yes |
| Hickey CA (1995)17 | 612 | 1.11 (0.61 to 2.11) | >3 vs ⩽3 h/d | 24–26 weeks | No | No | Yes | Yes* |
| Klebanoff MA (1990)21 | 7101 | 1.31 (1.01 to 1.71) | ⩾8 vs 0 h/d | 1–5 months | No | No | No | Yes |
| Launer LJ (1990)23 | 4168 | 1.56 (1.04 to 2.6) | Standing vs sitting | Not stated | No | No | No | No |
| Magann EF (2005)26 | 485 | 1.64 (0.88 to 3.06) | ⩾4 vs <4 h/d | Trimester 1 | No | No | No | No |
| Misra DP (1998)32 | 1166 | 1.05 (0.63 to 1.71) | ⩾3 vs <3 h/d | Trimesters 1 and 2 | No | Yes | No | Yes* |
| Newman RB (2001)33 | 1218 | 1.69 (1.2 to 2.38) | >3 vs ⩽3 h/d | 22–24 weeks | No | No | No | Yes |
| Pompeii LA (2005)38 | 977 | 1.2 (0.9 to 1.7) | >30 vs 6–15 h/wk | Trimester 1 | No | No | Yes | — |
| Pompeii LA (2005)38 | 977 | 0.9 (0.6 to 1.2) | >30 vs 6–15 h/wk | Trimester 2 | No | No | Yes | Yes§ |
| Pompeii LA (2005)38 | 977 | 1.3 (0.8 to 2.3) | >30 vs 6–15 h/wk | Trimester 3 | No | No | Yes | — |
| Teitelman AM (1990)51 | 708 | 2.72 (1.24 to 5.95) | Standing still >3 h/d vs continuous active motion | Trimester 1 (mostly) | No | No | No | Yes |
| Tuntiseranee P (1998)52 | 1121 | 0.9 (0.3 to 2.3) | ⩾5 vs ⩽4 h/d | 15–28 weeks | No | No | No | No |
| Case–control studies | ||||||||
| Berkowitz GS (1983)7 | 186 | 1.36 (0.73 to 2.55) | Most/all of the time vs none/little of the time | Not stated | No | Yes | No | Yes* |
| Hartikainen-Sorri AL (1989)15 | 358 | 1.16 (0.71 to 1.9) | Standing-moving vs not | Not stated | No | Yes | No | No |
| Luke B† (1995)24 | 1470 | 2.42 (1.37 to 4.62) | >4 vs <4 h/d | Not stated | Yes | No | No | No |
| Saurel-Cubizolles MJ (2004)45 | 4810 | 1.26 (1.1 to 1.5) | >6 vs <2 h/d | Trimester 1 | No | No | Yes | Yes* |
| Cross-sectional studies | ||||||||
| Ceron-Mireles P (1996)11 | 2429 | 1.16 (0.89 to 1.51) | >7 vs ⩽7 h/d | Not stated | No | No | No | No |
| Fortier I (1995)13 | 3502 | 0.88 (0.59 to 1.33) | ⩾6 vs <3 h/d | Not stated | No | No | No | Yes |
| Mamelle N (1984)27 | 1928 | 1.6 (1.0 to 1.9) | ⩾3 vs <3 h/d | Not stated | No | Yes | Yes | Yes* |
| McDonald AD (1988)29 | 22761 | 1.07, p>0.05 | Standing ⩾8 vs <8 h/d | Not stated | No | No | No‡ | No |
| Saurel-Cubizolles MJ (1987)43 | 2269 | 1.29 (0.85 to 1.94) | Standing (yes vs no) | Trimester 1 | No | Yes | Yes | No |
| Saurel-Cubizolles MJ (1991)44 | 874 | 1.59 (0.82 to 3.19) | Standing (often/always vs none/sometimes) | Not stated | No | No | Yes | Yes* |