Detection Rate for Heart Defects

Congenital heart disease is the most common serious birth defect.  It is more frequent than spinal cord defects (spina bifida) and Down syndrome. 

Congenital heart defects are more common than spina bifida and Down syndrome.

When serious heart defects are identified before birth, studies have demonstrated that the outcome of the newborn may be improved, especially for defects involving the left side of the heart and those of the outflow tracts.  One of the problems, however, is the identification of the fetus with a congenital heart defect.  At the present time over 90% of fetuses with serious heart defects may go undetected because of the limited experience of the physician or sonographer performing the screening examination of the heart. However, when the fetal heart is examined by specialists, known as Fetal Echocardiographers, the detection rate for congenital heart defects exceeds 90%.  Therefore, the problem is the following: “How can the fetus with a heart defect be identified so that a cardiac examination can be performed by a Fetal Echocardiographer?”

There are several solutions to this problem which are as follows:

1. First-trimester Nuchal Translucency Screening

Investigators have reported an association between an increased nuchal translucency measurement and the increased risk for congenital heart defects. One explanation for this association is that as the blood flow patterns are altered by the cardiac defect, congestion or other changes occur that manifests as an increase in size of the measured nuchal translucency.

2. Second-Trimester Genetic Ultrasound

This study is performed between 17 and 20 weeks of pregnancy and detects over 90% of fetuses with heart defects.

3. Third-Trimester 4D Fetal Heart and Face Screening Program

This examination of the heart occurs in the third trimester, between 24 and 32 weeks of pregnancy. This is a new program created by Dr. DeVore and is useful, especially for patients that cannot be referred for 1st trimester nuchal translucency screening or 2nd trimester Genetic Ultrasound, because it can identify defects of the heart, face, and abnormal growth.

 

What Percentage of Serious Heart Defects are Identified as the Result of an Increased Nuchal Translucency?

In 2005 Makrydimas et al published their results from a pooled database in which the nuchal translucency was measured during the first-trimester in 637 fetuses with congenital heart defects.  The fetuses were divided into two groups; those with abnormal chromosomes and those with normal chromosomes.  When the nuchal translucency was 3.5 mm or greater, 59% of fetuses with heart defects and abnormal chromosomes were identified.  Similarly, of fetuses with normal chromosomes, 23% with heart defects were identified because of an increased nuchal translucency measurement.

 

What Types of Heart Defects are Identified When the Nuchal Translucency is Increased in Size?

In the study by Makrydimas et al, they found that all major categories of heart defects were identified when the nuchal translucency measurement was 3.5 mm or greater.  The subgroups included the following:

*   Left heart lesions
*   Right Heart Lesions
*   Septal Defects
*   Outflow Tract Abnormalities
*   Abnormal Pulmonary Vein Drainage
*  Complex Heart Defect (More than one of the above findings)

When Should a Patient Be Referred for Fetal Echocardiography?

While the study by Makrydimas et al used a cutoff of 3.5 mm or greater, others have used a cutoff of 2.5 mm or greater.  The following graph illustrates the results of a study by Bahado-Singh et al published in 2005 in which the incidence of congenital heart defects is compared to the nuchal translucency measurement.  It can be seen that a dramatic increase in the incidence of heart defects occurs when the nuchal translucency measurement exceeds 3.5 mm.  In other studies investigators have lowered the threshold for examining the heart when the nuchal translucency is 2.5 mm or greater.  Therefore, if one were to use a conservative approach, a fetus with a nuchal translucency measurement of 2.5 mm or greater should be referred for fetal echocardiography.

 

Incidence of congenital heart defects based upon the measurement of the nuchal translucency measurement.

If a Fetus Is At Risk For A Congenital Heart Defect Because of an Increased Nuchal Translucency, When Should Fetal Echocardiography Be Performed?

Ideally, the referral should occur soon after the increased nuchal translucency is identified. However, some physicians may await the results of the chromosomal analysis before referring the patient for fetal heart studies.  Although first-trimester fetal echocardiography can be performed, it requires great skill of the examiner familiar with performing this type of study. In an opinion paper by Dr. DeVore in 2002, he reviewed a study by Huggon et al and suggested that it was time to consider offering patients prenatal diagnosis to detect heart defects during the 1st trimester of pregnancy. If the 1st trimester examination of the heart appears to be normal, then a repeat study at 20 weeks is indicated to identify malformations of the heart that may not have been identified with the 1st trimester study.  In a study reported by Becker and Wegner in 2006, they identified 84.2% of fetuses with congenital heart defects during the first-trimester examination when a specialist in fetal echocardiography performed the evaluation.