Transient foramen ovale incompetence in the normal newborn: an echocardiographic study

To assess presence, predominant direction and natural history of interatrial shunt flow in the normal newborn period an uncontrolled pilot study was performed. Twenty term ( > 36 completed weeks gestational age) newborns were studied using cross sectional, M-mode and colour Doppler echocardiography; cardiac, pulmonary or renal disease were excluded before entry to the study. In 11 of 20 normal term newborns a predominant left to right interatrial shunt was detected on the 1st day after birth. This shunting, taking place in ventricular systole, disappeared in 10 cases during the first 6 postnatal days and in 1 case after 6 weeks. No relation was found between the presence of an atrial left to right shunt and gestational age or patency of the ductus arteriosus.

We conclude that interatrial left to right shunting is common in half of the normal newborns (95% confidence interval 31.5%-76.9%), during the first 6 days of extra-uterine life. Our findings may be explained by a transient period of physiological expansion of extracellular volume in the newborn, resulting in slight atrial stretch, and this in combination with a relatively short foramen ovale flap.