Population based nationwide study of hypospadias in Sweden, 1973 to 2009: incidence and risk factors

Abstract

Purpose: We studied the incidence of hypospadias in Sweden during a 40-year period to determine if changes were associated with known risk factors.

Materials and methods: We analyzed prospective data from nationwide health care and demographic registers collected for all males (1,948,591 total) born in Sweden between 1973 and 2009. The incidence of hypospadias per 1,000 live-born boys was calculated as number of cases divided by total number of births yearly. The association between hypospadias and risk factors was estimated using logistic regression, expressed as odds ratios.

Results: The nationwide incidence of boys diagnosed with hypospadias was approximately 4.5 per 1,000 live-born boys until 1990, increasing to 8 per 1,000 boys during the following decade. Mild and severe phenotypes comprised the increase. Boys born small for gestational age (OR 4.34), as a twin (OR 1.8), as a result of in vitro fertilization (OR 1.15), or with parents from Asia (OR 1.45) or continental Europe (OR 1.41) were at increased risk for hypospadias. Multivariate analyses revealed that changes in risk factors did not explain the increased incidence. However, a systematic change in the classification of the diagnosis in registers could not be ruled out.

Conclusions: This nationwide study demonstrates an increased incidence of hypospadias diagnoses in Sweden from 1990 to 1999 that is not attributable to previously known risk factors. The increase includes mild and severe phenotypes, suggesting that shifts in the diagnostic criteria are not the underlying cause.

Keywords: birth weight; cohort studies; ethnic groups; hypospadias; incidence.