Background: Ambiguous sex has a great phenotypic variability and is a serious medical and social problem.
Aim: To study the prevalence of ambiguous sex among newborns.
Material and methods: As part of the ECLAMC (Cooperative Latin American Study of Congenital Malformations) all newborns with malformations are registered and the next normal newborn is considered as a control.
Results: 50.253 births occurred (between 1982 and 1999) in the University of Chile Maternity Hospital. The rate of congenital malformations was 6.78% and the prevalence of ambiguous sex was 4.7 per 10.000 births. Affected children had a lower birth weight, lower gestational age and a lower maternal age than controls. The most frequent associated malformations were of the urinary (64%) and cardiovascular systems (60.7%). Thirty two percent of affected children had specific syndromes.
Conclusions: The prevalence of ambiguous sex in this study was 4.7 per 10.000 births, which is higher than that reported in the ECLAMC (1.9 per 10,000).