CNS malformations in the Kraków region. I. Birth prevalence and seasonal incidence during 1979-1981.

The birth prevalence of CNS malformations in the region of Krakow from 1979 to 1981 was determined to be 1.26/1000 from records of all live- and still-birth deliveries. The frequency of anencephaly was 0.23/1,000; spina bifida and encephalocele, 0.70/1000; isolated hydrocephaly, 0.26/1,000; and other CNS anomalies, 0.06/1,000. The observed rates are below the median European level. Female preponderance was found among the probands with anencephaly, encephalomeningocele, and myelomeningocele. Cytogenetic examination of 35 newborns with CNS malformations documented normal karyotypes in all neonates. The analysis of seasonal distribution of proband's birthdate and of date of mother's last menstrual period showed no significant seasonal trend.