Ultrasound examination of the fetal heart was first reported in the early 1980’s when 2D technology allowed the examiner to identify the four-chambers of the fetal heart. Although the value of prenatal detection of heart defects was appreciated in a theoretical sense, it has only recently been realized as a benefit. The reason for this is that the ability to detect heart defects by the physician and/or sonographer has improved as the result of training and experience.
Recent studies have demonstrated that prenatal diagnosis of fetuses with heart defects improves the immediate outcome following delivery because they were born at tertiary hospitals. The benefit of delivery at such facilities is that the newborn baby can be evaluated and prepared for life-saving surgery. The three types of malformations in which prenatal diagnosis has been shown to be beneficial are Coarctation of the Aorta, Hypoplastic Left Ventricle, and Transposition of the Great Arteries. Each of these defects are discussed below.
The narrowed segment called coarctation can occur anywhere in the aorta, but is most likely to happen in the segment just after the aortic arch. This narrowing restricts the amount of oxygen-rich (red) blood that can travel to the lower part of the body. Varying degrees of narrowing can occur. The more severe the narrowing, the more symptomatic a child will be, and the earlier the problem will be noticed. In some cases, coarctation is noted in infancy. In others, however, it may not be noted until school-age or adolescence. Seventy-five percent of children with coarctation of the aorta also have a bicuspid aortic valve - a valve that has two leaflets instead of the usual three. Coarctation of the aorta occurs in about 8 percent to 11 percent of all children with congenital heart disease. Boys have the defect twice as often as girls do. (Lucile Packard Children's Hospital, Stanford, CA)
Hypoplastic left heart syndrome (HLHS) is a combination of several abnormalities of the heart and great blood vessels. It is a congenital (present at birth) syndrome, meaning that the heart defects occur due to abnormal underdevelopment of sections of the fetal heart during the first 8 weeks of pregnancy. In the normal heart, oxygen-poor (blue) blood returns to the right atrium from the body, travels to the right ventricle, then is pumped through the pulmonary artery into the lungs where it receives oxygen. Oxygen-rich (red) blood returns to the left atrium from the lungs, passes into the left ventricle, and then is pumped out to the body through the aorta. (Lucile Packard Children's Hospital, Stanford, CA)
In transposition of the great arteries, the aorta is connected to the right ventricle, and the pulmonary artery is connected to the left ventricle - the exact opposite of a normal heart's anatomy. Oxygen-poor (blue) blood returns to the right atrium from the body, passes through the right atrium and ventricle, then goes into the misconnected aorta back to the body. Oxygen-rich (red) blood returns to the left atrium from the lungs, passes through the left atrium and ventricle, then goes into the pulmonary artery and back to the lungs. Two separate circuits are formed - one that circulates oxygen-poor (blue) blood from the body back to the body, and another that recirculates oxygen-rich (red) blood from the lungs back to the lungs. (Lucile Packard Children's Hospital, Stanford, CA)
From Dr. DeVore’s experience prenatal diagnosis has been of great help in planning and preparing the mother and family members for optimal outcome of an unborn baby with a heart defect.
The following is from a website from the Lucile Packard Children's Hospital, at Stanford University that provides more information relating to congenital heart defects:
"Eight out of every 1,000 babies born in the United States have a congenital (present at birth) heart defect - a problem that occurred as the baby's heart was developing during pregnancy, before the baby is born. Congenital heart defects are the most common birth defects.
A baby's heart begins to develop at conception, but is completely formed by eight weeks into the pregnancy. Congenital heart defects happen during this crucial first eight weeks of the baby's development. Specific steps must take place in order for the heart to form correctly. Often, congenital heart defects are a result of one of these crucial steps not happening at the right time, leaving a hole where a dividing wall should have formed, or a single blood vessel where two ought to be, for example.
What causes congenital heart disease?
The vast majority of congenital heart defects have no known cause. Mothers will often wonder if something they did during the pregnancy caused the heart problem. In most cases, nothing can be attributed to the heart defect. Some heart problems do occur more often in families, so there may be a genetic link to some heart defects. Some heart problems are likely to occur if the mother had a disease while pregnant and was taking medications, such as anti-seizure medicines. However, most of the time, there is no identifiable reason as to why the heart defect occurred.
Congenital heart problems range from simple to complex.
Some heart problems can be watched by the baby's physician and managed with medicines, while others will require surgery, sometimes as soon as in the first few hours after birth. A baby may even "grow out" of some of the simpler heart problems, such as patent ductus arteriosus (PDA) or atrial septal defect (ASD), since these defects may simply close up on their own with growth. Other babies will have a combination of defects and require several operations throughout their lives.
What are the different types of congenital heart defects?
We can classify congenital heart defects into several categories in order to better understand the problems the baby will experience. They include:
Problems that cause too much blood to pass through the lungs
These defects allow oxygen-rich blood that should be traveling to the body to re-circulate through the lungs, causing increased pressure and stress in the lungs.
Problems that cause too little blood to pass through the lungs
These defects allow blood that has not been to the lungs to pick up oxygen (and, therefore, is oxygen-poor) to travel to the body. The body does not receive enough oxygen with these heart problems, and the baby will be cyanotic, or have a blue coloring.
Problems that cause too little blood to travel to the body
These defects are a result of underdeveloped chambers of the heart or blockages in blood vessels that prevent the proper amount of blood from traveling to the body to meet its needs."