Trends in the incidence of cryptorchidism and hypospadias, and methodological limitations of registry-based data.

Cryptorchidism and hypospadias share possible risk factors, such as intrauterine growth retardation. According to the data collected by the International Clearinghouse for Birth Defects Monitoring Systems (ICBDMS), apparently increasing trends in the incidence of hypospadias were found in Sweden during the 1960s, and in Norway, Denmark, England and Hungary during the 1970s. In Norway and Denmark, the increase continued in the 1980s, while in the USA it has continued from the 1970s to the 1990s. Finland has shown a lower reported rate of hypospadias than other Nordic countries. However, it is difficult to make comparisons between countries because of variable inclusion criteria. Furthermore, the reliability of the data depends on correct ascertainment and reporting of the cases. The ICBDMS has also collected data on cryptorchidism, but these appear to be unreliable because of a discrepancy with the data from cohort studies. According to two comparable English studies, the incidence of cryptorchidism in full-term boys approximately doubled between the 1950s and the 1980s. Regionally there are large differences: e.g. in Finland the incidence of cryptorchidism is clearly lower than in Denmark. Regional and temporal trends may help to identify environmental factors that might be associated with these disorders.