Objective: To quantify the normal distance between the insertion of the medial leaflets of the mitral valve and tricuspid valve in the fetal heart. This mitral valve-tricuspid valve distance was compared with the distance from known cases of Ebstein anomaly.
Methods: An apical 4-chamber view was obtained at end diastole in fetuses between 18 and 41 weeks' gestation. Calipers were placed parallel to the ventricular septum, with 1 caliper on the medial insertion of the mitral valve and a second caliper on the medial insertion of the tricuspid valve. The distance recorded was plotted against gestational age. Statistical analysis was performed by descriptive and linear regression techniques.
Results: One hundred forty-five fetuses were studied. The mean +/- SD mitral valve-tricuspid valve distance in the second trimester was 2.8 +/- 0.9 mm with a range of 1.2 to 5.0 mm; in the third trimester it was 4.6 +/- 1.1 mm with a range of 2.2 to 6.9 mm. Regression analysis showed that with each 1-week increase in gestational age, there was an increase of 0.15 mm in separation between the medial leaflets of the mitral valve and tricuspid valve (beta = 0.15 +/- 0.011).
Conclusions: A positive correlation between mitral valve-tricuspid valve distance and advancing gestational age was found. The reference range described allows for the identification of a fetal heart with normal variation in the mitral valve-tricuspid valve distance. Further downward displacement of the medial tricuspid cusp suggests the possibility of Ebstein anomaly.