Detection Rate of Down Syndrome Using Color Doppler Ultrasound

Ultrasound has been used in obstetrics for over three decades, and has not been demonstrated to be harmful. B-Mode ultrasound demonstrates anatomical features of the fetus (see section on B-Mode ultrasound). However, to evaluate the presence and direction of blood flow in the heart and vessels, color Doppler ultrasound has been used. Color Doppler displays blood flow in two basic colors. Red or Red-Orange displays blood flowing towards the top of the screen, and Blue displays flow towards the bottom of the screen. The use of color Doppler for evaluating the fetus at risk for Down syndrome was first reported by Dr. DeVore in 1995. In this study he found that examination of the fetal heart with color Doppler identified 87% of fetuses with Down syndrome. 
In a larger study reported in 2000 in which 2,000 normal fetuses were compared to 80 fetuses with Down syndrome, Dr. DeVore found that the use of color Doppler increased the detection rate for Down syndrome to 91%.

Color Doppler is useful in four areas when examining the heart of the fetus at risk for Down syndrome; ventricular septal defects, tricuspid regurgitation, chamber disproportion, and pericardial effusion.

 

Ventricular Septal Defect

In the majority of fetuses examined in the second trimester ventricular septal defects are not identified using B-Mode ultrasound. Color Doppler is essential to identify this type of heart defect. The image on the left demonstrates a normal four-chamber view with blood entering the ventricular chambers during diastole. Notice no blood is crossing the interventricular septum. . The image on the right demonstrates a ventricular septal defect in which blood is flowing across the ventricular septum.

Tricuspid Regurgitation

The image on the left demonstrates what appears to be a normal heart using B-Mode ultrasound. However, when the color Doppler is activated, tricuspid regurgitation is identified in the right atrial chamber. This fetus had Down syndrome.

Chamber Disproportion

Color Doppler is very useful for identifying the size of the atrial and ventricular chambers, especially in difficult to image fetuses. This clearly identifies blood entering the right and left atrial and ventricular chambers demonstrating chamber disproportion. In fetuses with Down syndrome, the right atrial chamber is often larger than the left atrial chamber.

Pericardial Effusion

In the second-trimester fetus the pericardial space may be difficult to image. However, with the use of color Doppler ultrasound, fluid can be observed moving within the pericardial space.


Detection of Down Syndrome using B-Mode and Color Doppler Ultrasound and Computation of Risk Following Genetic Ultrasound


If you would like to see how the risk for Down syndrome is computed following a Genetic Sonogram, CLICK HERE. 



91% Detection Rate for Down Syndrome. In a study published by Dr. DeVore, he reported that the detection rate for Down syndrome was dependent upon which of the above ultrasound abnormalities were detected by the physician. For example, if the physician was unable to evaluate the fetal heart, but could examine the fetal head and abdomen, then 60% of fetuses with Down syndrome would be detected. If the heart is examined, and the physician only checks for the presence or absence of atrial and/or ventricular septal disproportion, then the detection rate would increase to 75%. When color Doppler is added and the physician examines the heart thoroughly, then the detection rate for Down syndrome increases to 91%. Conversely, if this type of ultrasound is normal, then the risk for Down syndrome can be reduced by 90%. The following table lists the ultrasound findings and their corresponding Likelihood Ratios. The likelihood ratio is the number that the risk for Down syndrome is increased when an abnormal finding is present. 


*Likelihood ratio is the number that the risk for Down syndrome is increased when an abnormal ultrasound finding is present. To compute the risk for Down syndrome the Likelihood Ratio is multiplied by the risk for Down syndrome prior to the test.