Annual and seasonal variations in the prevalence of congenital cardiac malformations in live-born infants

The annual and seasonal distribution of the prevalence of congenital cardiac malformations was calculated in 664,218 infants born from 1977 to 1984 in Bohemia (population of 6.3 million). All children who died were autopsied and those confirmed as having a malformation of the heart were included in our series. In total, 4,409 infants (6.64/1,000 live-births) were born with a cardiac defect. Annual variations were insignificant. The prevalence rate of cardiac malformations at birth was highest in October and lowest in December, June and July. It was not modified by differences in the birthrate. The peak of the prevalence coincided with the epidemics of influenza in early pregnancy. A nonuniform seasonal variation was found in individual forms of congenital malformations of the heart, indicating their possible etiological heterogeneity.