title: Physically demanding work and preterm delivery: a systematic review and meta-analysis.
abstract: OBJECTIVE
  Physically demanding work may increase the risk of preterm delivery (PTD), defined as delivery before 37 weeks. We assessed the available evidence.
  
  
  METHODS
  A systematic search in Medline, Embase and Nioshtic for the period 1990 to June 2012 for observational and intervention studies on physically demanding work (prolonged standing, heavy lifting, physical exertion, occupational fatigue and demanding posture) and PTD. Selected studies were assessed for their risk of bias and pooled using a random effects model. Results of case-control and cohort studies were reported separately in subgroups.
  
  
  RESULTS
  We found 10 studies with low risk of bias and seven studies with moderate risk of bias. Standing and walking at work during pregnancy for more than 3 h per day was associated with an increased risk for PTD [OR 1.3 (95% CI 1.1-1.6)], just as lifting and carrying >5 kg [OR 1.3 (95% CI 1.05-1.6)] or lifting and carrying in the third trimester of the pregnancy [OR 1.3 (95% CI 1.01-1.8)]. Jobs that required physical effort or physical exertion were associated with an increased risk of PTD [OR 1.4 (95% CI 1.19-1.66)]. Working during pregnancy in jobs with a combination of two or more physical tasks, physical effort or occupational fatigue was also associated with an increased risk of PTD [OR 1.5 (95% CI 1.1-2.0)].
  
  
  CONCLUSIONS
  Physically demanding work during pregnancy is associated with an increased risk of PTD, especially in jobs with a combination of tasks with physical effort. In general, only small to moderate elevations of risks were found.
authors.affiliation: Department of Occupational Health and Safety Service, DNV GL, P.O. Box 9035, 6800 ET, Arnhem, The Netherlands, monique.vanbeukering@dnvgl.com.
authors.forename: M D M
authors.initials: MD
authors.lastname: van Beukering
authors.forename: M J G J
authors.initials: MJ
authors.lastname: van Melick
authors.forename: B W
authors.initials: BW
authors.lastname: Mol
authors.forename: M H W
authors.initials: MH
authors.lastname: Frings-Dresen
authors.forename: C T J
authors.initials: CT
authors.lastname: Hulshof
mesh_terms: D005221:Fatigue / Q000503:physiopathology; D005260:Female; D006801:Humans; D009784:Occupational Diseases / Q000209:etiology / Q000503:physiopathology; D005082:Physical Exertion / Q000502:physiology*; D011247:Pregnancy; D047928:Premature Birth / Q000209:etiology*; D016474:Weight-Bearing / Q000502:physiology; D014937:Work / Q000502:physiology*