The normal offset of the tricuspid septal leaflet in the fetus.
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.
D004437:Ebstein Anomaly / Q000473:pathology*; D005260:Female; D005318:Fetal Heart / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D005865:Gestational Age; D006801:Humans; D008943:Mitral Valve / Q000196:embryology*; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011263:Pregnancy Trimester, Third; D012016:Reference Values; D014261:Tricuspid Valve / Q000196:embryology*; D016216:Ultrasonography, Prenatal