title: Occupational lifting, fetal death and preterm birth: findings from the Danish National Birth Cohort using a job exposure matrix.
abstract: OBJECTIVE
  We examined the association between occupational lifting during pregnancy and risk of fetal death and preterm birth using a job exposure matrix (JEM).
  
  
  METHODS
  For 68,086 occupationally active women in the Danish National Birth Cohort, interview information on occupational lifting was collected around gestational week 16. We established a JEM based on information from women, who were still pregnant when interviewed. The JEM provided mean total loads lifted per day within homogeneous exposure groups as informed by job and industry codes. All women were assigned an exposure estimate from the JEM. We used Cox regression models with gestational age as underlying time variable and adjustment for covariates.
  
  
  RESULTS
  We observed 2,717 fetal deaths and 3,128 preterm births within the study cohort. No exposure-response relation was observed for fetal death, but for women with a prior fetal death, we found a hazard ratio (HR) of 2.87 (95% CI 1.37, 6.01) for stillbirth (fetal death ≥22 completed gestational weeks) among those who lifted >200 kg/day. For preterm birth, we found an exposure-response relation for primigravid women, reaching a HR of 1.43 (95% CI 1.13, 1.80) for total loads >200 kg per day. These findings correspond to an excess fraction of 11% for stillbirth and 10% for preterm birth.
  
  
  CONCLUSIONS
  We found an increased risk of stillbirth among women with a prior fetal death, who lifted >200 kg/day, and an exposure-response relationship between occupational lifting and preterm birth among primigravid women. The study adds to a large body of prospective studies on occupational lifting and adverse pregnancy outcomes by refined exposure assessment.
authors.affiliation: Department of Occupational and Environmental Medicine, Bispebjerg Hospital, University of Copenhagen, Copehagen, Denmark.
authors.forename: Emina
authors.initials: E
authors.lastname: Mocevic
authors.affiliation: Danish Ramazzini Centre, University Department of Occupational Medicine, Herning Regional Hospital, Herning, Denmark.
authors.forename: Susanne Wulff
authors.initials: SW
authors.lastname: Svendsen
authors.affiliation: Department of Occupational and Environmental Medicine, Bispebjerg Hospital, University of Copenhagen, Copehagen, Denmark.
authors.forename: Kristian Tore
authors.initials: KT
authors.lastname: Jørgensen
authors.affiliation: Danish Ramazzini Centre, Department of Occupational Medicine, Aarhus University Hospital, Aarhus, Denmark.
authors.forename: Poul
authors.initials: P
authors.lastname: Frost
authors.affiliation: Department of Occupational and Environmental Medicine, Bispebjerg Hospital, University of Copenhagen, Copehagen, Denmark.
authors.forename: Jens Peter
authors.initials: JP
authors.lastname: Bonde
mesh_terms: D000293:Adolescent; D000328:Adult; D015331:Cohort Studies; D003718:Denmark / Q000453:epidemiology; D005260:Female; D005313:Fetal Death; D005865:Gestational Age; D006801:Humans; D017770:Lifting; D008875:Middle Aged; D016273:Occupational Exposure / Q000009:adverse effects*; D011247:Pregnancy; D011256:Pregnancy Outcome; D047928:Premature Birth / Q000453:epidemiology*; D016016:Proportional Hazards Models; D055815:Young Adult