Purpose: We studied risk factors for cryptorchidism and hypospadias.
Materials and methods: We performed a register based, case control study of 6,177 boys with cryptorchidism, 1,345 with hypospadias and 23,273 male controls born live in Denmark from 1983 to 1992 to determine the effects of cryptorchidism and hypospadias on the presence of the other abnormality in an individual, the presence of the abnormalities in an older brother, birth weight, weeks of gestation, maternal history of stillbirth, parity, twin birth, parental age, nationality and professional status. Unconditional logistic regression analysis was used to estimate odds ratios.
Results: In an individual simultaneous cryptorchidism and hypospadias were more common than expected. There was an increased risk of both entities when the same abnormality was present in an older brother. The risk of cryptorchidism and hypospadias increased with decreasing birth weight independent of weeks of gestation. Twins were at lower risk than singletons for both entities in all lower birth weight groups. An increased risk of hypospadias was noted in the sons of women who had had a previous stillbirth. The risk of cryptorchidism and hypospadias slightly increased with decreasing parity.
Conclusions: Birth weight was the principal determinant of cryptorchidism and hypospadias. Twins were at lower risk for both abnormalities than singletons in the same birth weight classes. There are indications of separate genetic as well as common environmental causes of cryptorchidism and hypospadias.