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147 TRANSIENT FORAMEN OVALE INCOMPETENCE IN NORMAL NEWBORNS

In contrast with the generally accepted mechanism of functional closure of the foramen ovale at birth, echocardiography studies in sick newborns revealed the presence of transient interatrial left to right shunts (IALRS) in several patients without structural heart disease. The aim of this study was to assess incidence and natural history of IALRS in healthy newborns. 20 healthy term newborns underwent an echocardiography and Doppler study daily during the first week after birth. Left atrial and aortic root dimensions were measured, as well as duration and direction of ductal and interatrial shunting. In 11 of these infants a predominant IALRS was detected on the first day of extrauterine life. In one infant IALRS persisted for as long as 6 weeks. Median persistance of IALRS in the remaining 10 infants was 3 days. Ductal left to right shunts were present in 3 infants with and in 2 without IALRS. There was no significant difference between infants with or without IARLS in respect to ductal patency, birthweight or sex. There was a statistically significant relation between lower gestational age and presence and duration of IALRS. We conclude that transient IALRS is common in normal newborns during the first week of extrauterine life. We suggest that this transient foramen ovale incompetence results from a relatively short foramen ovale flap in combination with the relative large extracellular volume as is present in the first days of life.