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Shift work and subfecundity: a causal link or an artefact?
J L Zhu1, N H Hjollund, H Boggild
1The Danish Epidemiology Science Centre, University of Aarhus, Vennelyst Boulevard 6, DK 8000 Aarhus C, Denmark.
Occupational and Environmental Medicine
|August 26, 2003
Summary
Shift work, particularly fixed evening or night shifts, showed a slight association with reduced fecundity, indicated by a longer time to pregnancy. However, no definitive causal link to subfecundity was established, suggesting potential bias in pregnancy planning.
Area of Science:
- Reproductive Epidemiology
- Occupational Health
- Human Fecundity Studies
Background:
- Shift work is prevalent and may impact reproductive health.
- Understanding the relationship between occupational schedules and fecundity is crucial for public health.
Purpose of the Study:
- To investigate the association between shift work and fecundity, measured by time to pregnancy (TTP).
- To determine if specific shift work patterns (fixed evening, fixed night, rotating) affect the ability to conceive.
Main Methods:
- Utilized data from the Danish National Birth Cohort (DNBC) including 17,531 daytime and 3,907 shift workers.
- Employed logistic regression and discrete time survival analysis to calculate fecundity odds ratios (ORs) for TTP.
- Controlled for potential confounders like age, BMI, smoking, and alcohol consumption.
Main Results:
- Fixed evening and fixed night shift workers experienced a longer TTP, indicating potentially reduced fecundity (ORs 0.80).
- Rotating shift work (with or without nights) showed no significant association with TTP.
- Higher rates of unplanned pregnancies and contraceptive failures were observed in fixed evening/night workers.
Conclusions:
- No conclusive evidence supports a causal link between shift work and subfecundity.
- Observed associations for fixed evening/night shifts may be influenced by pregnancy planning behaviors or reduced opportunities for conception.