Rotating shift work and menstrual cycle characteristics

Epidemiology. 2011 May;22(3):305-12. doi: 10.1097/EDE.0b013e3182130016.


Background: Shift workers who experience sleep disturbances and exposure to light at night could be at increased risk for alterations in physiologic functions that are circadian in nature.

Methods: We investigated rotating shift work and menstrual cycle patterns in the Nurses' Health Study II using cross-sectional data collected in 1993 from 71,077 nurses aged 28-45 years who were having menstrual periods and were not using oral contraceptives. Log-binomial regression was used to estimate relative risks (RRs) and 95% confidence intervals (CIs).

Results: Eight percent of participants reported working rotating night shifts for 1-9 months, 4% for 10-19 months, and 7% for 20+ months during the previous 2 years. Irregular cycles (>7 days variability) were reported by 10% of participants. Seventy percent of women reported menstrual cycles of 26-31 days, 1% less than 21 days, 16% 21-25 days, 11% 32-39 days, and 1% 40+ days. Women with 20+ months of rotating shift work were more likely to have irregular cycles (adjusted RR = 1.23 [CI = 1.14-1.33]); they were also more likely to have cycle length <21 days (1.27 [0.99-1.62]) or 40+ days (1.49 [1.19-1.87]) (both compared with 26-31 days). For irregular patterns and for 40+ day cycles, there was evidence of a dose response with increasing months of rotating shift work. Moderately short (21-25 days) or long (32-39 days) cycle lengths were not associated with rotating shift work.

Conclusions: Shift work was modestly associated with menstrual function, with possible implications for fertility and other cycle-related aspects of women's health.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adaptation, Physiological
  • Adult
  • Age Factors
  • Chronobiology Disorders / epidemiology*
  • Chronobiology Disorders / etiology
  • Chronobiology Disorders / physiopathology
  • Confidence Intervals
  • Cross-Sectional Studies
  • Female
  • Humans
  • Incidence
  • Linear Models
  • Menstrual Cycle / physiology*
  • Menstruation Disturbances / epidemiology*
  • Menstruation Disturbances / etiology
  • Menstruation Disturbances / physiopathology
  • Middle Aged
  • Multivariate Analysis
  • Nurses / statistics & numerical data*
  • Prognosis
  • Risk Assessment
  • Surveys and Questionnaires
  • Work Schedule Tolerance*