Epidemiology of ambiguous genitalia in South America.

We present descriptive epidemiologic data on ambiguous genitalia (AG), obtained in the period 1967-1982 by the Latin American Collaborative Study of Congenital Malformations (ECLAMC) through 70 participating hospitals located in 34 cities of 9 South American countries. The observed prevalence rate for isolated AG was about 1/20,000 births, with at least 1/4 and probably as much as 1/2 due to congenital adrenal hyperplasia. When AG cases associated with other congenital anomalies were also considered, the overall frequency of AG was 1/6,900 total births (1/10,000 for live and 1/350 for stillbirths). The prevalence rates were homogeneously distributed among the different countries, and there was a stable secular trend. AG was more frequent in nontropical than in tropical areas of South America, and there was a significant seasonal variation with its acrophase in August (winter). A case-control analysis of 14 risk factors showed an association of AG with a prenatal history of acute maternal illnesses. These data do not support an etiological relationship between AG and hypospadias.