Malformations Recorded on Birth Certificates following A2 Influenza Epidemics

Abstract

I NTEREST in the relationship of viral infections to malformations was first aroused by the discovery that the human embryo could be damaged by rubella (1), and several attempts were made in studies following the appearance and worldwide spread of Asian influenza, (type A2) in 1957-58 to determine whether this disea-se a,lso might be teratogenic. A review (2) of most of these studies suggested that their results were inconclusive. The reporte,d malformations in children whose mothers might have had influenza in early pregnancy were much less homogeneous than those observed in children following exposure to known teratogens such as rubella and thalidomide. Although statistically significant increases in the incidence of particular types of defects in such children were reported from Dublin, Ireland (3), and Birmingham, England (2, 4), the types of defects were different in the two cities. Anencephalus, meningocele, encephalocele, and spina bifida were especially common among the children of Dublin women who reported an attack of influenza during pregnancy. In Birmingham the incidence of cleft lip, esophageal atresia, anal atresia, and exomphalos, and especially of cases exhibiting combinations of these malformations with each other or with other defects, was significantly increased among children who had been in the early stages of intrauterine life when influenza was epidemic. Data from other sources apparently have not been examined for consistency with either set of findings. In this study we examined U.S. birth records for evidence of increases in the incidence of defects following influenza epidemics.