Congenital malformations co-occurring with hypospadias in California, 1983-1997.

Investigations for co-occurring malformations can serve as a first step to discover new risk factors and provide insights into malformation etiologies. Our objective was to explore the risks of occurrence of structural congenital malformation phenotypes in 5,481 infants with hypospadias, using data from a population-based active surveillance system. Ascertainment was performed among 1,816,258 liveborn and 12,203 stillborn male offspring of women who were residents of registry counties during 1983-1997. Malformations other than hypospadias were grouped according to the 3- and 4-digit BPA malformation codes. Prevalences of each malformation grouping were calculated among all births with hypospadias and their three subgroups and all births without hypospadias but with another structural malformation. Relative risks were estimated based on the ratio of two prevalences, and the corresponding 95% confidence intervals were computed using Poisson regression models. Observed relative risks indicated that all malformation groupings were less likely to co-occur with hypospadias and their three subgroups than with other types of malformations, with relative risks ranging from 0.04 to 0.93. For most malformations, risks were relatively similar among all births with hypospadias and the three subgroups of hypospadias. The observed relative risks were not substantially changed in analyses that adjusted for maternal age, race/ethnicity, and parity. Computations were extended to 4-digit level BPA codes. Almost all observed relative risks for malformations co-occurring with hypospadias overall and three subgroups were less than 1.