The value of England and Wales congenital malformation notification scheme data for epidemiology: male genital tract malformations.

Data from the England and Wales national congenital malformation notification scheme were examined for associations of male genital tract malformations. For some of the malformations comparison of notification rates with the literature suggested gross undernotification. There was also evidence suggesting bias: examination of the relationships of the malformations to birth weight, maternal parity, and maternal age at delivery showed some highly significant trends in risk, most of which were at variance with findings in the literature, and several potential mechanisms for bias could be adduced. Direct investigation is needed, for this and other similar data sets, of the extent and mechanisms of biased undernotification.