OBJECTIVE: To examine the relationship between occupational use of high level disinfectants among nurses and time to pregnancy (TTP). DESIGN: Prospective cohort study. MATERIALS AND METHODS: Our study included 2,581 women trying to become pregnant or with a recent planned pregnancy in the Nurses' Health Study 3 cohort (2010-present). Every 3 to 6 months women report the duration of their pregnancy attempt. Women were considered at risk of pregnancy for the duration of their pregnancy attempt until they became pregnant, stopped trying to become pregnant, or were lost to follow-up. Occupational exposure to agents used to disinfect medical instruments, devices, or supplies was self-reported on the baseline questionnaire. Multivariable Cox proportional hazards models for discrete survival time were used to estimate the fecundability odds ratios (FOR) and 95% confidence intervals (CI) adjusting for age, race, BMI, smoking, and marital status. RESULTS: Nurses who reported current exposure to high level disinfectants had a 22% reduction in fecundity (longer TTP) compared to nurses who were never exposed (FOR=0.78 [95% CI 0.67, 0.90]). A longer TTP was associated with current use of glutaraldehyde (FOR=0.77 [95% CI 0.62, 0.96]) but not with ortho-phthalaldehyde (FOR=1.02 [95% CI 0.66, 1.56]), peracetic acid (FOR=1.27 [95% CI 0.82, 1.97]), or hydrogen peroxide (FOR=0.74 [95% CI 0.54, 1.02]). Consistent use of R3 types of protective equipment was rare (6.7%) but significantly protected exposed women against longer TTPs. When specific types of equipment were examined, only consistent use of a water resistant gown or respiratory protection (not including surgical mask) significantly protected exposed women against longer TTPs. Use of a disinfection system with dedicated ventilation, eye protection, or protective gloves appeared to be beneficial however they did not reach statistical significance. CONCLUSION: Occupational use of high level disinfectants, particularly glutaraldehyde, is associated with reduced fertility among women. Nurses using high level disinfectants should be advised to use the recommended protective equipment as these might mitigate the fertility impairments associated with high level disinfectant use.