Shift Work as a Potential Risk Factor for Lower Ovarian Reserve: A Study of Fertility Patients

Background/Objectives: Shift work is a form of circadian dysregulation, which has been associated with adverse reproductive health outcomes. However, the association between circadian dysregulation and ovarian reserve remains uncertain. The present study examines whether shift work is associated with lower AMH levels in women seeking fertility treatment. Methods: This retrospective cohort study includes female patients aged 20–39 years presenting between February 2023 and June 2024. Patients were excluded if they had only one ovary, a current cancer diagnosis, or past chemotherapy use. Demographic and medical data were obtained from the electronic medical record. AMH levels were compared between daytime workers and shift workers. Results: A total of 1135 patients met inclusion criteria. The median age was 35 years (IQR 32–37). Of these, 89% (n = 1014) reported daytime work, and 11% (n = 121) reported shift work, comprising 102 working rotating shifts, seven working night shifts, and 12 working evening shifts. Daytime-only workers had a median AMH of 17.20 pmol/L (9.1–30.0). Combined shift workers had a median AMH of 17.10 pmol/L (8.1–31.0). There was no statistically significant difference in AMH levels between daytime workers and shift workers (p = 0.935). Although not significant, the odds of having low AMH levels (<7 pmol/L) were 25% higher among shift workers compared to daytime workers (OR 1.246, p = 0.345). Conclusions: In this cohort, AMH levels did not significantly differ between daytime and shift workers, offering reassurance to individuals required to engage in shift work. Future research should include larger cohorts and incorporate more comprehensive measures of circadian disruption.