Prevalence rates of microtia in South America.

A high frequency of microtia in Quito (Ecuador) was detected by the Latin American Collaborative Study of Congenital Malformations (ECLAMC), and the data available on file were used to define the cluster and to test some potential risk factors. The Quito material consisted of 46 041 livebirths from two hospitals. The rest of the sample consisted of 553 068 livebirths from 58 hospitals located in 24 cities of six other South American countries. The observed prevalence rate for microtia was over five times higher in Quito (17.4/10 000) than in the other cities (3.2/10 000). The microtias from Quito were mostly represented by isolated forms (without other anomalies except for preauricular tags and/or sinuses), and the proportion of severe microtia was higher than in the rest of the sample. Neither seasonal, nor secular variations were observed in Quito or the rest of the sample; data suggesting the geographical cluster did not arise in recent years. Case-control analysis of familial, prenatal and perinatal history data in 184 cases with isolated microtia (68 from Quito and 116 from the rest) and in 184 matched non-malformed control newborn babies, identified prenatal drug exposure, high birth order, and elevated paternal age as risk factors for the microtias born in Quito.