Geographical differences in the prevalence of hypospadias in Finland.

Hypospadias is one of the most common congenital anomalies but the etiology is not fully understood. There seem to be genetic, endocrinological, and environmental factors involved. Great geographical variation in the prevalence of hypospadias has been reported both between and within countries. We studied the determinants of geographical variation in the prevalence of hypospadias in Finland. All patients treated for hypospadias in 1970-1996 before the age of 9 years among boys born in 1970-1986 were identified in the national hospital discharge registry. Prevalence of hypospadias was calculated for each of the 355 municipalities in Finland. Demographic data were obtained from Statistics Finland. Association of the explanatory factors with prevalence of hypospadias was assessed using Poisson regression methods. The prevalence of operated hypospadias varied between provinces and between university hospital districts, from a ratio of 0.65 to a ratio of 1.01. An association between the prevalence of hypospadias and the remoteness from the closest city was observed. There was no association with level of education, social class, or occupation. The observed differences in the prevalence of operated hypospadias in Finland may have several explanations. Different levels of ascertainment and both genetic and environmental factors can not be ruled out.