Night work during pregnancy and risk of cryptorchidism among male offspring: A Danish nationwide register-based cohort study.

Aim: The aim was to investigate the association between night work during pregnancy and the risk of having a male offspring with cryptorchidism. Furthermore, we explored if the risk of cryptorchidism increased based on trimester-specific night work (gestational weeks 1-12 and 13-22) by sensitivity analyses.

Methods: This register-based cohort study was based on detailed objective working hour data for all employees in the five Danish regions (primarily hospital employees) between 2007 and 2015, retrieved from the Danish Working Hour Database (DWDH). Information on pregnancies and covariates was identified by linking DWDH with the Danish Medical Birth Register. Diagnoses of cryptorchidism were obtained from the Danish National Patient Register. We used logistic regression to investigate the association between different dimensions of night work during the first 32 pregnancy weeks and cryptorchidism. The adjusted models included maternal age, body mass index, socioeconomic position, and maternal smoking.

Results: The final cohort consisted of 12,915 singleton pregnancies in 11,404 women (primarily nurses), who worked at least one night shift during the first 32 pregnancy weeks. None of the dimensions of night work was associated with an increased risk of having offspring with cryptorchidism compared to day workers. We found the same tendency in the trimester-specific analyses.

Conclusions: We found no increased odds among women working night shifts in healthcare during pregnancy and giving birth to male offspring with cryptorchidism. Future studies investigating night work in occupations other than healthcare are needed to rule out a potential association.