To estimate the change of discharge rate after cryptorchidism surgery between pre- and postdisaster in Japan. Cryptorchidism cannot be diagnosed before birth and is not a factor that would influence a woman's decision to seek an abortion. Therefore, this disease is considered suitable for assessing how the Great East Japan Earthquake and the subsequent Fukushima Daiichi nuclear accident (2011) influenced congenital diseases.

We obtained cryptorchidism discharge data collected over 6 years from hospitals that were included in an impact assessment survey of the Diagnosis Procedure Combination survey database in Japan and used these data to estimate the discharge rate after cryptorchidism surgery before and after the disaster. The 94 hospitals in Japan that participated in Diagnosis Procedure Combination system and had 10 or more discharges after cryptorchidism surgery within successive 6 years covering pre- and postdisaster period (FY2010-FY2015) were involved. The change in discharge rate between pre- and postdisaster was analyzed using a Bayesian generalized linear mixed model.

Nationwide, a 13.4% (95% credible interval 4.7%-23.0%) increase in discharge rates was estimated. The results of all sensitivity analyses were similar to the reported main results.

The discharge rate of cryptorchidism was increased nationwide. The rates of low-weight babies or preterm births, risk factors of cryptorchidism, were almost constant during the study period, and age distribution of the surgery was also not changed, which suggested that the other factors that associated with the disaster increased the incidence of cryptorchidism.