Relationship between working hours, standing, shift work and two pregnancy outcomes (preterm delivery and small for gestational age): meta-estimates of relative risk (1966–2011)*
| Working hours (> vs <40 h/week) | Standing (>4 vs <4 h/day) | Shift work (Yes vs No) | ||||
|---|---|---|---|---|---|---|
| N | RR (95% CI) | N | RR (95% CI) | N | RR (95% CI) | |
| Preterm delivery | ||||||
| Overall meta-estimate | 17 | 1.23 (1.13 to 1.34) | 12 | 1.22 (1.12 to 1.33) | 19 | 1.14 (1.01 to 1.30) |
| Sensitivity analysis† | 11 | 1.18 (1.05 to 1.33) | 7 | 1.13 (0.99 to 1.29) | 12 | 1.04 (0.94 to 1.15) |
| Later pregnancy | 6 | 1.17 (0.94 to 1.45) | 7 | 1.15 (0.96 to 1.37) | 8 | 1.17 (0.86 to 1.60) |
| SGA | ||||||
| Overall meta-estimate | 8 | 1.04 (0.94 to 1.16) | 7 | 1.07 (0.94 to 1.22) | 10 | 1.01 (0.92 to 1.10) |
| Sensitivity analysis† | 6 | 0.99 (0.88 to 1.11) | 5 | 1.16 (0.97 to 1.38) | 7 | 0.98 (0.90 to 1.08) |
| Later pregnancy | 4 | 0.99 (0.83 to 1.19) | 5 | 0.95 (0.76 to 1.20) | 5 | 1.05 (0.94 to 1.18) |
*See online supplementary tables S1 and S2 for details of the reports and risk estimates incorporated into these meta-analyses.
†Excluding studies with a higher potential for bias or confounding, or which reported incompletely.
RR, relative risk; SGA, small for gestational age