Question: what is the cause of congenital heart defects

Reference:
 Congenital heart defects in children Overview If your child has a congenital heart defect, it means that your child was born with a problem in the structure of his or her heart. Some congenital heart defects in children are simple and don't need treatment. Other congenital heart defects in children are more complex and may require several surgeries performed over a period of several years. Learning about your child's congenital heart defect can help you understand the condition and know what you can expect in the coming months and years. Congenital heart defect care at Mayo Clinic Symptoms Serious congenital heart defects usually become evident soon after birth or during the first few months of life. Signs and symptoms could include: - Pale gray or blue skin color (cyanosis) - Rapid breathing - Swelling in the legs, abdomen or areas around the eyes - Shortness of breath during feedings, leading to poor weight gain Less serious congenital heart defects may not be diagnosed until later in childhood, because your child may not have any noticeable signs of a problem. If signs and symptoms are evident in older children, they may include: - Easily becoming short of breath during exercise or activity - Easily tiring during exercise or activity - Fainting during exercise or activity - Swelling in the hands, ankles or feet Serious congenital heart defects are often diagnosed before or soon after your child is born. If you notice that your baby has any of the signs or symptoms above, call your child's doctor. If your child has any of the signs or symptoms of less serious heart defects as he or she grows, call your child's doctor. Your child's doctor can let you know if your child's symptoms are due to a heart defect or another medical condition. Causes The heart is divided into four hollow chambers, two on the right and two on the left. To pump blood throughout the body, the heart uses its left and right sides for different tasks. The right side of the heart moves blood to the lungs through vessels called pulmonary arteries. In the lungs, blood picks up oxygen then returns to the heart's left side through the pulmonary veins. The left side of the heart then pumps the blood through the aorta and out to the rest of the body. During the first six weeks of pregnancy, the heart begins taking shape and starts beating. The major blood vessels that run to and from the heart also begin to form during this critical time during gestation. It's at this point in your baby's development that heart defects may begin to develop. Researchers aren't sure exactly what causes most of these defects, but they think genetics, certain medical conditions, some medications and environmental factors, such as smoking, may play a role. There are many different types of congenital heart defects, falling mainly into these categories: - Holes in the heart. Holes can form in the walls between heart chambers or between major blood vessels leaving the heart. In certain situations, these holes allow oxygen-poor blood to mix with oxygen-rich blood, resulting in less oxygen being carried to your child's body. Depending on the size of the hole, this lack of sufficient oxygen can cause your child's skin or fingernails to appear blue or possibly lead to congestive heart failure. A ventricular septal defect is a hole in the wall between the right and left chambers on the lower half of the heart (ventricles). An atrial septal defect occurs when there's a hole between the upper heart chambers (atria). Patent ductus arteriosus (PAY-tunt DUK-tus ahr-teer-e-O-sus) is a connection between the pulmonary artery (containing deoxygenated blood) and the aorta (containing oxygenated blood). A complete atrioventricular canal defect is a condition that causes a hole in the center of the heart. - Obstructed blood flow. When blood vessels or heart valves are narrow because of a heart defect, the heart must work harder to pump blood through them. Eventually, this leads to enlarging of the heart and thickening of the heart muscle. Examples of this type of defect are pulmonary stenosis or aortic stenosis (stuh-NO-sis). - Abnormal blood vessels. Several congenital heart defects happen when blood vessels going to and from the heart don't form correctly, or they're not positioned the way they're supposed to be. A defect called transposition of the great arteries occurs when the pulmonary artery and the aorta are on the wrong sides of the heart. A condition called coarctation of the aorta happens when the main blood vessel supplying blood to the body is too narrow. Total anomalous pulmonary venous connection is a defect that occurs when blood vessels from the lungs attach to wrong area of the heart. - Heart valve abnormalities. If the heart valves can't open and close correctly, blood can't flow smoothly. One example of this type of defect is called Ebstein's anomaly. In Ebstein's anomaly, the tricuspid valve - which is located between the right atrium and the right ventricle - is malformed and often leaks. Another example is pulmonary atresia, in which the pulmonary valve is missing, causing abnormal blood flow to the lungs. - An underdeveloped heart. Sometimes, a major portion of the heart fails to develop properly. For example, in hypoplastic left heart syndrome, the left side of the heart hasn't developed enough to effectively pump enough blood to the body. - A combination of defects. Some infants are born with several heart defects. Tetralogy of Fallot (teh-TRAL-uh-jee of fuh-LOW) is a combination of four defects: a hole in the wall between the heart's ventricles, a narrowed passage between the right ventricle and pulmonary artery, a shift in the connection of the aorta to the heart, and thickened muscle in the right ventricle. Risk factors Most congenital heart defects result from problems early in your child's heart development, the cause of which is unknown. However, certain environmental and genetic risk factors may play a role. They include: - Rubella (German measles). Having rubella during pregnancy can cause problems in your baby's heart development. Your doctor can test you for immunity to this viral disease before pregnancy and vaccinate you against it if you aren't immune. - Diabetes. You can reduce the risk of congenital heart defects by carefully controlling your diabetes before attempting to conceive and during pregnancy. Gestational diabetes generally doesn't increase your baby's risk of developing a heart defect. - Medications. Certain medications taken during pregnancy may cause birth defects, including congenital heart defects. Give your doctor a complete list of medications you take before attempting to become pregnant. Medications known to increase the risk of congenital heart defects include thalidomide (Thalomid), angiotensin-converting enzyme (ACE) inhibitors, statins, the acne medication isotretinoin (Absorica, Amnesteem, Claravis) and lithium. - Drinking alcohol during pregnancy. Avoid alcohol during pregnancy because it increases the risk of congenital heart defects. - Smoking. Smoking during pregnancy increases the likelihood of a congenital heart defect in the baby. - Heredity. Congenital heart defects sometimes run in families and may be associated with a genetic syndrome. Many children with Down syndrome - which is caused by an extra 21st chromosome (trisomy 21) - have heart defects. A missing piece (deletion) of genetic material on chromosome 22 also causes heart defects. Genetic testing can detect such disorders during fetal development. If you already have a child with a congenital heart defect, a genetic counselor can estimate the odds that your next child will have one. Complications Some potential complications that can occur with a congenital heart defect include: - Congestive heart failure. This serious complication may develop in babies who have a significant heart defect. Signs of congestive heart failure include rapid breathing, often with gasping breaths, and poor weight gain. - Slower growth and development. Children with more-serious congenital heart defects often develop and grow more slowly than do children who don't have heart defects. They may be smaller than other children of the same age and, if the nervous system has been affected, may learn to walk and talk later than other children. - Heart rhythm problems. Heart rhythm problems (arrhythmias) can be caused by a congenital heart defect or from scarring that forms after surgery to correct a congenital heart defect. - Cyanosis. If your child's heart defect causes oxygen-poor blood to mix with oxygen-rich blood in his or her heart, your child may develop a grayish-blue skin color, a condition called cyanosis. - Stroke. Although uncommon, some children with congenital heart defects are at increased risk of stroke due to blood clots traveling through a hole in the heart and on to the brain. - Emotional issues. Some children with congenital heart defects may feel insecure or develop emotional problems because of their size, activity restrictions or learning difficulties. Talk to your child's doctor if you're concerned about your child's moods. - A need for lifelong follow-up. Children who have heart defects should be mindful of their heart problems their entire lives, as their defect could lead to an increased risk of heart tissue infection (endocarditis), heart failure or heart valve problems. Most children with congenital heart defects will need to be seen regularly by a cardiologist throughout life. Diagnosis Your child's doctor may initially suspect a problem because he or she hears a heart murmur during a routine exam. A heart murmur is a sound that occurs when blood flows through the heart or blood vessels fast enough to make a sound that a doctor can hear with a stethoscope. Most heart murmurs are innocent, meaning that there is no heart defect and the murmur isn't dangerous to your child's health. Some murmurs, however, may mean blood is flowing through your child's heart abnormally because he or she has a heart defect. Tests to diagnose a congenital heart defect If it's possible your child has a heart defect, your doctor or your child's doctor may order several tests to see if your child has a heart problem. In addition to a regular physical exam, these could include: - Fetal echocardiogram. This test allows your doctor to see if your child has a heart defect before he or she is born, allowing your doctor to better plan treatment. In this test, your doctor performs an ultrasound. The sound waves from the ultrasound are used to create a picture of your baby's heart. - Echocardiogram. Your child's doctor may use a regular echocardiogram to diagnose a congenital heart defect after your child has been born. In this noninvasive test, your child's doctor performs an ultrasound to produce images of the heart. An echocardiogram allows the doctor to see your child's heart in motion and to identify abnormalities in the heart muscle and valves. - Electrocardiogram. This noninvasive test records the electrical activity of your child's heart and can help diagnose heart defects or rhythm problems. Electrodes connected to a computer and printer are placed on your baby's chest and show waves that indicate how your child's heart is beating. - Chest X-ray. Your child may have a chest X-ray to see if the heart is enlarged, or if the lungs have extra blood or other fluid in them. These could be signs of heart failure. - Pulse oximetry. This test measures how much oxygen is in your child's blood. A sensor is placed over the end of your child's finger to record the amount of oxygen in your child's blood. Too little oxygen could suggest your child has a heart problem. - Cardiac catheterization. In this test, a thin, flexible tube (catheter) is inserted into a blood vessel at your baby's groin and guided through it into the heart. Catheterization is sometimes necessary because it may give your child's doctor a much more detailed view of your child's heart defect than an echocardiogram. In addition, some treatment procedures can be done during cardiac catheterization. - Cardiovascular magnetic resonance imaging (MRI). This type of imaging is becoming increasingly used to diagnose and evaluate congenital heart defects in adolescents and adults. Newer MRI technology provides faster imaging and higher resolution than other methods, such as echocardiography. Treatment A congenital heart defect may have no long-term effect on your child's health - in some instances, such defects can safely go untreated. Certain defects, such as small holes, may even correct themselves as your child ages. Some heart defects, however, are serious and require treatment soon after they're found. Depending on the type of heart defect your child has, doctors treat congenital heart defects with: - Procedures using catheterization. Some children and adults now have their congenital heart defects repaired using catheterization techniques, which allow the repair to be done without surgically opening the chest and heart. Catheter procedures can often be used to fix holes or areas of narrowing. In procedures that can be done using catheterization, the doctor inserts a thin tube (catheter) into a leg vein and guides it to the heart with the help of X-ray images. Once the catheter is positioned at the site of the defect, tiny tools are threaded through the catheter to the heart to repair the defect. - Open-heart surgery. Depending on your child's condition, he or she may need surgery to repair the defect. Many congenital heart defects are corrected using open-heart surgery. In open-heart surgery, the chest has to be opened. In some cases, minimally invasive heart surgery may be an option. This type of surgery involves making small incisions between the ribs and inserting instruments through them to repair the defect. - Heart transplant. If a serious heart defect can't be repaired, a heart transplant may be an option. - Medications. Some mild congenital heart defects, especially those found later in childhood or adulthood, can be treated with medications that help the heart work more efficiently. Drugs known as angiotensin-converting enzyme (ACE) inhibitors, angiotensin II receptor blockers (ARBs) and beta blockers and medications that cause fluid loss (diuretics) can help ease stress on the heart by lowering blood pressure, heart rate and the amount of fluid in the chest. Certain medications can also be prescribed to help irregular heartbeats (arrhythmias). Sometimes, a combination of treatments is necessary. In addition, some catheter or surgical procedures have to be done in steps, over a period of years. Others may need to be repeated as a child grows. Long-term treatment Some children with congenital heart defects require multiple procedures and surgeries throughout life. Although the outcomes for children with heart defects have improved dramatically, most people, except those with very simple defects, will require ongoing care, even after corrective surgery. - Lifelong monitoring and treatment. Even if your child has surgery to treat a heart defect, your child's condition will need to be monitored for the rest of his or her life. Initially, your child with a congenital heart defect will be monitored and have regular follow-up appointments with a pediatric cardiologist. As your child grows older, his or her care will transition to an adult congenital cardiologist, who can monitor his or her condition over time. A congenital heart defect can affect your child's adult life, as it can contribute to other health problems. Adults who have congenital heart defects may need other treatments for their condition. As your child ages, it's important to remind him or her of the heart condition that was corrected and the need for ongoing, lifelong care by doctors experienced in evaluating and treating congenital heart disease. Encourage your child to keep his or her doctor informed about the heart defect and the procedures performed to treat the problem. - Exercise restrictions. Parents of children with congenital heart defects may worry about the risks of rough play and activity even after treatment. Although some children may need to limit the amount or type of exercise, many can participate in normal or near-normal activity. Your child's doctor can tell you which activities are safe for your child. If some activities do pose distinct dangers, encourage your child to participate in other activities instead of focusing on what he or she can't do. Although every child is different, most children with congenital heart defects grow up to lead healthy, productive lives. - Infection prevention. Depending on the type of congenital heart defect your child had, and the surgery used to correct it, your child may need to take extra steps to prevent infection. Sometimes, a congenital heart defect can increase the risk of infections - either in the lining of the heart or heart valves (infective endocarditis). Because of this risk, your child may need to take antibiotics to prevent infection before additional surgeries or dental procedures. Children who are most likely to have a higher risk of infection include those whose defect was repaired with a prosthetic material or device, such as an artificial heart valve. Ask your child's cardiologist if preventive antibiotics are necessary for your child. 

Answer: Most congenital heart defects result from problems early in your child's heart development, the cause of which is unknown. However, certain environmental and genetic risk factors may play a role. They include: - Rubella (German measles).  Having rubella during pregnancy can cause problems in your baby's heart development.  Diabetes. You can reduce the risk of congenital heart defects by carefully controlling your diabetes before attempting to conceive and during pregnancy.  Certain medications taken during pregnancy may cause birth defects, including congenital heart defects. Medications known to increase the risk of congenital heart defects include thalidomide (Thalomid), angiotensin-converting enzyme (ACE) inhibitors, statins, the acne medication isotretinoin (Absorica, Amnesteem, Claravis) and lithium. - Drinking alcohol during pregnancy. Smoking during pregnancy increases the likelihood of a congenital heart defect in the baby. - Heredity. Congenital heart defects sometimes run in families and may be associated with a genetic syndrome. Many children with Down syndrome - which is caused by an extra 21st chromosome (trisomy 21) - have heart defects. A missing piece (deletion) of genetic material on chromosome 22 also causes heart defects. Genetic testing can detect such disorders during fetal development.  a genetic counselor can estimate the odds that your next child will have one.