Evaluation of normal fetal atrio-ventricular septum dimensions during pregnancy

Ebstein anomaly and atrio-ventricular septal defect involve a profound change in the appearance of the atrio-ventricular septum (AVS). AVS is the area between the insertion of the mitral valve and the tricuspid valve leaflets to the ventricular septum. In normal fetuses, the tricuspid valve has an apical displacement relative to the mitral valve. We aimed to create a nomogram of its normal dimensions, beginning in the 11th gestational week.

Measurement of the length of the AVS was performed during ultrasonographic fetal echocardiography, in the four-chamber view from 11 to 34 gestational weeks in otherwise normal pregnancies. In addition, standard fetal biometry was measured. Linear regression analysis was used to evaluate the correlation between variables.

Two hundred and ninety-two examinations of normal fetuses were included. A positive correlation was found between AVS length and gestational age (r(2) = 0.96, P < 0.001), each week adding 0.165 mm (β = 0.165, P < 0.001). AVS length was also proportional to inter-ventricular septum (IVS) length with increasing gestational age (r(2) = 0.882, β = 0.94, P < 0.001). Positive linear correlation was obtained between AVS length and fetal biometry (P < 0.001).

We provide a nomogram for AVS length which can be used as a reference when either Ebstein anomaly or atrio-ventricular septal defects are suspected.