Objectives The Danish National Birth Cohort was used to examine whether laboratory work was associated with reduced fecundity.

Methods Self-reported data on laboratory work and waiting time to pregnancy (0–2, 3–5, 6–12 and >12 months) were used for 829 female laboratory technicians interviewed in 1997–2003. Altogether 6250 female teachers formed the reference group. A discrete-time survival analysis with a complementary log-log link was applied to estimate the fecundability ratio between the exposed and unexposed women, with adjustment for maternal age, gravidity, smoking, prepregnancy body mass index, and paternal job.

Results No difference in time to pregnancy was found between the laboratory technicians and teachers or between the laboratory technicians with different exposures. The adjusted fecundability ratio for the laboratory technicians was 0.94 [95% confidence interval (95% CI) 0.86–1.02] for all pregnancies and 0.98 (95% CI 0.86–1.13) for first pregnancies. A healthy worker effect was found for the laboratory technicians working with the work processes under study.

Conclusions The results do not suggest that laboratory work in Denmark at present impairs female fecundity.

Key terms Denmark; exposure; fecundability; fecundity; female; laboratory technician; national birth cohort; time to pregnancy