title: Influence of shift work on early reproductive outcomes: a systematic review and meta-analysis.
abstract: OBJECTIVE
  To determine whether an association exists between shift work and early reproductive outcomes.
  
  
  METHODS
  MEDLINE, Embase, and Web of Science were searched. Additional sources included Google Scholar, the Cochrane Library, online publications of national colleges, the ClinicalTrials.gov, and references of retrieved papers.
  
  
  METHODS
  Included studies compared female shift workers (work outside 8:00 AM to 6:00 PM) with nonshift workers with menstrual disruption (cycles less than 25 days or greater than 31 days), infertility (time-to-pregnancy exceeding 12 months), or early spontaneous pregnancy loss (less than 25 weeks).
  
  
  RESULTS
  Two reviewers extracted adjusted and raw data. Random effect models were used to pool data weighting for the inverse of variance. Assessments of heterogeneity, bias, and subgroup analyses were performed. Sixteen independent cohorts from 15 studies (123,403 women) were subject to analysis. Shift workers had increased rates of menstrual disruption (16.05% [2,207/13,749] compared with 13.05% [7,561/57,932] [n=71.681, odds ratio {OR} 1.22, 95% confidence interval {CI} 1.15-1.29, I 0%]) and infertility (11.3% [529/4,668] compared with 9.9% [2,354/23,811] [OR 1.80, 95% CI 1.01-3.20, I 94%]) but not early spontaneous pregnancy loss (11.84% [939/7,931] compared with 12.11% [1,898/15,673] [n=23,604, OR 0.96, 95% CI 0.88-1.05, I 0%]). Night shifts were associated with increased early spontaneous pregnancy loss (n=13,018, OR 1.29, 95% CI 1.11-1.50, I 0%). Confounder adjustment led to persistent relationships between shift work and menstrual disruption (adjusted OR 1.15, 95% CI 1.01-1.31, I 70%) but not infertility (adjusted OR 1.11 95% CI 0.86-1.44, I 61%). The association between night shifts and early spontaneous pregnancy loss remained (adjusted OR 1.41 95% CI 1.22-1.63, I 0%).
  
  
  CONCLUSIONS
  This review provides evidence for an association between performing shift work and early reproductive outcomes, consistent with later pregnancy findings. However, there is currently insufficient evidence for clinicians to advise restricting shift work in women of reproductive age.
authors.affiliation: University of Southampton, Faculty of Medicine, Academic Unit of Human Development and Health, Southampton, and Kings College London, Women's Academic Health Centre, St. Thomas' Hospital, London, United Kingdom.
authors.forename: Linden J
authors.initials: LJ
authors.lastname: Stocker
authors.forename: Nicholas S
authors.initials: NS
authors.lastname: Macklon
authors.forename: Ying C
authors.initials: YC
authors.lastname: Cheong
authors.forename: Susan J
authors.initials: SJ
authors.lastname: Bewley
mesh_terms: D000022:Abortion, Spontaneous / Q000453:epidemiology / Q000209:etiology*; D005260:Female; D006801:Humans; D007247:Infertility, Female / Q000453:epidemiology / Q000209:etiology*; D008599:Menstruation Disturbances / Q000453:epidemiology / Q000209:etiology*; D010561:Personnel Staffing and Scheduling / Q000706:statistics & numerical data*; D011247:Pregnancy; D012098:Reproduction; D018570:Risk Assessment; D014940:Work Schedule Tolerance