Seasonality in live births with congenital heart disease in Malta.

This study was carried out to analyse seasonal variations in live births with congenital heart disease in the overall population of Malta. Included were all patients diagnosed as having congenital heart disease by echocardiography, cardiac catheterization, surgery or post mortem, by 1 year of age, and who were born between in Malta between 1990 and 1994. Results were analysed by X2 and by Edwards' cyclic method. There were 231 cases of live born congenital heart disease, which were divided into 114 cases not requiring intervention and 117 cases requiring intervention. Although the overall prevalence of congenital heart disease did not demonstrate any seasonal variation, the lesions requiring intervention showed a significant peak in September by Edwards' method (p = 0.03), which was enhanced by seasonal analysis (p = 0.003). These results were confirmed by conventional X2 and X2 for trend. The lesions not requiring intervention, which were comprised almost entirely (96%) of mild pulmonary stenosis and small ventricular septal defects, failed to show any seasonal trend. The literature regarding such seasonal trends in these malformations and statistical analysis of seasonality of congenital heart disease are reviewed. An environmental factor such as a maternal viral infection or treatment of such infections during the first trimester of pregnancy from November to January may precipitate congenital heart disease in predisposed Maltese foetuses.