The anatomical variability of the membranous septum in the normal human fetal heart is due to the size and shape of the septal components.

The article reports on an investigation into the dimensions and shape variability of the atrioventricular and interventricular components of the membranous septum in human fetal hearts at 17-28 weeks. Using stereomicroscope with digital camera and software, we studied 80 normal specimens. In the 17-28 weeks group, the membranous septum length was 1.6±0.78 mm. The atrioventricular component was present in 86.25% of cases, while the interventricular component was present in 73.75% of cases. The length of the atrioventricular component was 0.9 mm at 17-19 weeks, and 1.2 mm at 26-28 weeks. The atrioventricular height increased from 0.75 mm at 17-19 weeks to 1.53 mm at 26-28 weeks. The interventricular component had equal median lengths of 0.57-0.60 mm in the 20-28 weeks group. Its height at 17-22 weeks was 0.75 mm, reaching 1.0 mm at 20-22 weeks, and increasing by no more than 10% in older groups. There were no correlations between atrioventricular or interventricular length and height that indicated great variability of the components in shape. For the atrioventricular component, common shapes were round, oval, and triangular. The interventricular component was mostly round or vertically oval; in some cases, it appeared as a horizontal oval or a vertical slit. The data may be useful for intracardiac fetal surgery, for example, in correction of hypoplastic aortic root and closure of interventricular communication, as well as for connective tissue three-dimensional bioprinting in cardiac abnormalities.