Mitral valve-tricuspid valve distance as a sonographic marker of trisomy 21.

OBJECTIVE

Pathologic studies suggest that a decreased mitral valve-tricuspid valve distance (MTD) is found in trisomy 21 fetuses without cardiac defects. We assessed the feasibility of using the MTD as a second-trimester sonographic marker for trisomy 21.

METHODS

We performed a retrospective case-control study of all cases of trisomy 21 at our institution from 1998 to 2008. Cases without a prenatally identified cardiac defect and with adequate images from 15 to 26 weeks' gestation were assessed. The distance between the medial insertions of the mitral and tricuspid valves (i.e. the MTD) onto the ventricular septum was obtained. We also obtained the MTD from normal controls during the study period. Multiple linear regression analysis was used to assess the effects of gestational age and trisomy 21 on MTD. Gestational age-specific percentiles and multiples of the median were calculated, and curves were fitted using linear regression analysis.

RESULTS

We identified 57 trisomy 21 fetuses with a measurable MTD and compared these with 634 control fetuses. Multiple linear regression analysis revealed a positive correlation between MTD and gestational age and a negative correlation between trisomy 21 and MTD. Using a cut-off of the 5(th) percentile, the MTD detected 70% of trisomy 21 cases with a 3.8% false-positive rate in the controls.

CONCLUSIONS

The MTD increases with gestational age and is lower in fetuses with trisomy 21. Twenty (35%) of the 57 cases had no sonographic marker of trisomy 21 except an MTD below the 5(th) percentile for gestational age. The MTD was a useful independent marker for trisomy 21 in the second trimester.