Mobility of the flap valve of the primary atrial septum in the developing human fetus

It has already been suggested that redundancy of the primary atrial septum could be associated with primary fetal arrhythmias. There are few reports, however, concerning the mobility of the primary septum and its behavior during fetal life. In this study, fifteen fetuses without anatomic heart disease were serially evaluated by fetal echocardiography. The time interval between three separate examinations was at least two weeks. A redundancy index was calculated as the ratio between the maximum excursion of the flap valve of the septum and the maximal left atrium as seen in a four chamber view. The indexes observed in the three examinations were: 0.55 +/- 0.15, 0.48 +/- 0.13 and 0.41 +/- 0.13, respectively. Analysis of variance for normal distribution and Tukey's test were performed. A significant decrease (p < 0.05) in the redundancy index was observed with increasing gestational age. We postulate that this finding may be related to the decrease in frequency of premature atrial beats throughout fetal life.