THE EPIDEMIOLOGY OF OROFACIAL CLEFTS .1. SOME GENERAL EPIDEMIOLOGIC CHARACTERISTICS

Using data from three registries of congenital anomalies based on a to tal of more than 5 million births, some epidemiological characteristic s were studied for 8,315 infants with cleft lip and/or cleft palate. T here was a racial variation in the rate of cleft lip/palate within the California program but also a marked difference in rate between the t hree programs-France, Sweden, and California-that is probably not main ly a result of variable ascertainment but of real differences between the populations, The main analysis was made on cases without a known c hromosome anomaly. The classical sex distribution was found with an ex cess of males at cleft lip/palate. The sex ratio was lower (= more nor mal) when associated nonfacial malformations existed. Pierre Robin typ e cleft palate had a near-normal sex distribution while other types of cleft palate had the usual excess of females. Twinning was increased for all facial clefts irrespective of type but was more common when no nfacial associated malformations were present than when the cleft was isolated. Among cases with isolated clefts, the total twin increase wa s not statistically significant but the proportion of monozygotic twin s was increased. There was a U-shaped maternal age relationship for cl eft lip/palate that was not seen for median cleft palate (although an indicated increased risk for infants of teen-age mothers existed). For all types of cleft, there was an increased risk at high parity also a fter standardization for maternal age.