Fetal echocardiography provides a valuable means to better understand intrauterine growth and development of the heart and great vessels. The prenatal diagnosis of structural heart disease and the physiologic evaluation of fetal arrhythmias are perhaps the most important insights provided by this technique. The long-term effects of ultrasound energy on the developing fetus, however, are unknown. This fact may be particularly important when the higher energy levels associated with Doppler techniques are used.
To date, no detrimental effects in humans have been demonstrated. Still, it is advisable to avoid excess exposure of the fetus by keeping the examination time as short as possible and using the lowest possible power setting. There are several potential indications for performing fetal echocardiography. Evaluation of the heart in the setting of retarded fetal growth or fetal distress is often recommended. Whenever extracardiac anomalies are detected during fetal ultrasound examination, cardiac assessment may be beneficial. The presence of chromosomal abnormalities detected with amniocentesis is strongly correlated with congenital heart disease and is another accepted indication for fetal echocardiography.
The test should also be performed as part of the assessment of fetal arrhythmias. Finally, whenever congenital heart disease is suspected for other reasons, such as maternal exposure to teratogenic substances or a parental history of previous children with congenital lesions, the examination should be considered.
The performance of a fetal echocardiogram requires experience and a systematic approach. Guidelines for training have been formulated, and only qualified individuals should perform this highly specialized examination. A brief description of the examination is presented here for interest only. The first step is to determine the position and orientation of the fetus within the uterus. Within the thorax, the heart, because of its motion, is usually the easiest and most recognizable structure to examine.
The four-chamber view is most important and should be recorded first For orientation, the left atrium is identified by the presence of the septum primum and the pulmonary veins. Cardiac situs can be determined by identifying the systemic veins and the position of the atria relative to the liver and spleen. Next, the atrioventricular valves are identified, with the tricuspid valve slightly more apical than the mitral valve. The outlet portions of the heart are then evaluated. Cardiac measurements can be made and compared with normal values that have been defined for all gestational ages.
Doppler techniques can be used to visualize blood flow through the heart, great vessels, and umbilical vessels. Assessment of fetal arrhythmias is best accomplished by using a combination of M-mode and Doppler recordings. When these arrhythmias are present, a careful search for structural heart disease is mandatory. With this approach, a wealth of diagnostic information is available. Knowledge of complex congenital heart disease before delivery allows therapeutic interventions to begin immediately after birth and can be life saving for such patients. In both of these examples, knowledge about the presence and severity of congenital cardiac defects facilitated management of labor and delivery and allowed perinatal care to be optimized.
The critical role of echocardiography in prenatal diagnosis is evident, and both the accuracy and safety of the test are now well established. The structures in these images are small, however, and random movements of the fetus make for a challenging and time-consuming examination. Despite these factors, fetal echocardiography has provided clinicians with earlier diagnosis of heart disease and a better understanding of fetal hemodynamics.
Today, a dedicated fetal echocardiogram can detect nearly 100% of serious congenital heart disease. Yet most pregnant women do not have a fetal echocardiogram but rather undergo a general obstetric ultrasound that may detect only around a third of fetal heart disease. To improve detection, some propose universal fetal echocardiography (http://www.ncbi.nlm.nih.gov/pubmed/18029923). But others cite cost and lack of specialized personnel as barriers that prevent echocardiography for every fetus (http://www.ncbi.nlm.nih.gov/pubmed/18029914).
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