title: Work schedule and physical factors in relation to fecundity in nurses.
abstract: OBJECTIVE
  To evaluate the association of work schedule and physical factors with fecundity.
  
  
  METHODS
  Women currently employed outside the home and trying to get pregnant (n=1739) in the Nurses' Health Study 3 cohort (2010-2014) were included in this analysis. Work schedule and physical labour were self-reported on the baseline questionnaire, and every 6 months thereafter the women reported the duration of their ongoing pregnancy attempt. Multivariable accelerated failure time models were used to estimate time ratios (TR) and 95% CIs.
  
  
  RESULTS
  Among the 1739 women (median age=33 years, 93% Caucasian) the estimated proportions of women not pregnant after 12 and 24 months were 16% and 5%, respectively. None of the various shift work patterns were associated with duration of pregnancy attempt (as a surrogate for fecundity). However, women working >40 h/week had a 20% (95% CI 7 to 35%) longer median duration of pregnancy attempt compared to women working 21-40 h/week (p-trend=0.005). Women whose work entailed heavy lifting or moving (ie, 25+ pounds) >15 times/day also had a longer median duration of pregnancy attempt (adjusted TR=1.49; 95% CI 1.20 to 1.85) compared to women who never lifted or moved heavy loads (p-trend=0.002). The association between heavy moving and lifting and duration of pregnancy attempt was more pronounced among overweight or obese women (body mass index, BMI<25: TR=1.17; 95% CI 0.88 to 1.56; BMI≥25: TR=2.03, 95% CI 1.48 to 2.79; p-interaction=0.007).
  
  
  CONCLUSIONS
  Working greater than 40 h per week and greater frequency of lifting or moving a heavy load were associated with reduced fecundity in a cohort of nurses planning pregnancy.
authors.affiliation: Department of Nutrition, Harvard T.H. Chan School of Public Health, Boston, Massachusetts, USA Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, Massachusetts, USA.
authors.forename: Audrey J
authors.initials: AJ
authors.lastname: Gaskins
authors.affiliation: Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, Massachusetts, USA Channing Division of Network Medicine, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts, USA Department of Medicine, Connors Center for Women's Health and Gender Biology, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Janet W
authors.initials: JW
authors.lastname: Rich-Edwards
authors.affiliation: National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention, Cincinnati, Ohio, USA.
authors.forename: Christina C
authors.initials: CC
authors.lastname: Lawson
authors.affiliation: Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, Massachusetts, USA Channing Division of Network Medicine, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Eva S
authors.initials: ES
authors.lastname: Schernhammer
authors.affiliation: Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, Massachusetts, USA Channing Division of Network Medicine, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts, USA Department of Obstetrics, Gynecology and Reproductive Biology, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Stacey A
authors.initials: SA
authors.lastname: Missmer
authors.affiliation: Department of Nutrition, Harvard T.H. Chan School of Public Health, Boston, Massachusetts, USA Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, Massachusetts, USA Channing Division of Network Medicine, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Jorge E
authors.initials: JE
authors.lastname: Chavarro
mesh_terms: D000328:Adult; D015992:Body Mass Index; D005260:Female; D005298:Fertility; D006801:Humans; D007247:Infertility, Female / Q000209:etiology*; D017770:Lifting / Q000009:adverse effects*; D009726:Nurses; D009765:Obesity / Q000150:complications; D016273:Occupational Exposure / Q000009:adverse effects*; D011247:Pregnancy; D011795:Surveys and Questionnaires; D014937:Work; D014940:Work Schedule Tolerance
keywords: Fertility < Methodology, speciality; Physical work < Materials, exposures and occupational groups