The epidemiology of orofacial clefts. 1. Some general epidemiological characteristics.

Using data from three registries of congenital anomalies based on a total of more than 5 million births, some epidemiological characteristics were studied for 8,315 infants with cleft lip and/or cleft palate. There was a racial variation in the rate of cleft lip/palate within the California program but also a marked difference in rate between the three programs-France, Sweden, and California-that is probably not mainly a result of variable ascertainment but of real differences between the populations. The main analysis was made on cases without a known chromosome anomaly. The classical sex distribution was found with an excess of males at cleft lip/ palate. The sex ratio was lower (= more normal) when associated nonfacial malformations existed. Pierre Robin type 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 nonfacial associated malformations were present than when the cleft was isolated. Among cases with isolated clefts, the total twin increase was not statistically significant but the proportion of monozygotic twins was increased. There was a U-shaped maternal age relationship for cleft 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 after standardization for maternal age.