Fetal echocardiography refers to a detailed examination of the fetal heart, over and above the careful screening of the heart which we perform during every ultrasound scan.
With our genetic sonogram, we start out by checking the size, position, and rate of the heart. The heart should be about the size of a dime placed upon a quarter, should be in the left chest, should beat with a rate between about 120 and 160 most of the time, and should show us all four chambers – the left and right atria and left and right ventricles. The dividing line between the atria and ventricles should point at about a 45-degree angle toward the left side of the chest.
We then look to make certain that the great vessels above the heart – the superior vena cava, aorta, and pulmonary artery – have a normal spatial and size relationship.
We also try to obtain images showing the aorta leaving the heart, with normal aortic size and a normal aortic arch, and images showing the pulmonary artery leaving the heart in a normal orientation, and feeding into the ductus arteriosus. The combination of these views will detect 75% or more of fetal heart defects. These are described in more detail below.
About Major Heart Defects
Major heart defects occur in between 0.5 and 1 percent of the population. In pregnancies that are at increased risk for heart defects, either based upon a history of a heart defect in the family, an exposure to a drug or medication that can affect the development of the heart, or an enlarged nuchal translucency or nuchal skin fold, a detailed heart ultrasound, or echocardiogram, is recommended.
A complete fetal echocardiogram excludes about 80 to 90 percent of major cardiac defects. The most common abnormalities that could be missed on a fetal echocardiogram are small atrial and ventricular septal defects. Also, it is not possible to exclude some acquired heart abnormalities, such as failure of one side of the heart or the other to grow, or narrowing of the aorta or pulmonary artery, which can occur later in the pregnancy even though baby’s heart appears normal at the time of a fetal echocardiogram.
Our goal is always to push ultrasound technology in detection of birth defects right to the cutting edge. For families with increased risk for certain types of heart defects, we offer fetal echocardiography at the 13- to 14-week pregnancy mark. Specific types of heart defects which we can assess that early include hypoplastic left and hypoplastic right hearts, tetralogy of Fallot, atrial or ventricular septal defects, and transposition of the great arteries.
Depending on your body characteristics, whether you have had surgeries involving the uterus or lower abdomen in the past, and the positioning of your baby, we may be able to obtain a crisp set of cardiac views even at 13 or 14 weeks, either by transabdominal or transvaginal sonography, and we have been able to exclude major defects in many cases. In other pregnancies, either maternal factors or an uncooperative baby will prevent us from being able to obtain the set of images that we want. In either case, we will still recommend a detailed fetal echocardiogram at the 22-week mark, since our ability to predict/detect congenital heart defects is lower in early pregnancies.
Views of the Baby’s Heart
If we use only the four-chamber view to assess the baby’s heart, then we will identify about 50 percent of babies with major heart defects. The American Institute of Ultrasound in Medicine recommends that every ultrasound scan include a check of the aorta and pulmonary artery as they leave the heart. The aorta carries blood from the left ventricle of the heart to the body, and the pulmonary artery carries blood from the right side of the heart; in the adult, the pulmonary artery leads from the heart to the lungs.
Our Center performs three more standard views of the heart – a “great vessels” view above the level of the heart, showing the aorta, pulmonary artery, and superior vena cava (the large blood vessel that brings blood back from the head and neck into the heart), as well as the arch of the aorta and the ductus arteriosus. The combination of these six views of the heart in our genetic sonogram would be expected to identify about 75 percent of major heart defects.
The Fetal Echocardiogram
In addition to the standard heart views, we obtain measurements of the ventricles of the heart, of the aorta and pulmonary artery, and also measure the blood flow through these structures. We obtain images showing the veins entering the heart: the pulmonary veins that enter the left atrium of the heart and the inferior vena cava and superior vena cava, which enter the right atrium.
Finally, we look with color mapping techniques to show that blood is flowing in the correct direction into the atria, from the atria to the ventricles, and from the ventricles out through the aorta and pulmonary artery. Color mapping techniques are also used to assess for any gaps or defects in the ventricular septum, and to make sure that the atrial septum shows a normal valve, called the foramen ovale, permitting blood to flow from the right atrium to left atrium, bypassing the lungs, while baby is still inside.
What if a Cardiac Abnormality is Found?
First, we will perform a comprehensive evaluation of the baby, to assess for any other abnormalities. Because most cardiac defects carry a markedly increased risk that the baby has a chromosomal problem, we will arrange genetic counseling and offer genetic amniocentesis testing. Presuming that the baby has no other abnormalities and normal chromosomes, we will then recommend and arrange a fetal echocardiogram with the pediatric heart specialists at Rady Children’s Hospital-San Diego, who can provide you with greater detail about the nature of the abnormality, and develop a treatment plan for the pregnancy.
If you have specific concerns about your baby having a congenital cardiac defect, either based upon a prior pregnancy affected by congenital heart disease, others in the family, such as yourself or your husband, who have had surgery for a heart defect, or drug or medication exposures, then please contact our office early in the pregnancy for genetic counseling, and to decide whether a detailed fetal heart ultrasound will be recommended.