What causes a congenital heart defect (CHD)?

A congenital heart defect (CHD) is a heart problem that a baby has at birth. It is caused by abnormal formation of the heart during growth in the womb. In most cases, when a baby is born with a congenital heart defect, there is no known reason for it. Some types of congenital heart defects can be linked to an abnormality in the number of a baby’s chromosomes. They may be linked to single gene defects. Or they may be linked to environmental factors. In most cases, there is no clear cause that can be found for the heart defect. They are often thought to be caused by many factors. The factors are usually both genes and the environment. This means that genes from both parents plus unknown environmental factors lead to the problem.

Birth parent factors and CHDs

Most cases of congenital heart defect have no known cause. But some types of congenital heart defects occur more often when the birth parent comes in contact with some types of substances in the first few weeks of pregnancy. This is the time when the baby's heart is growing. Some illnesses a mother may have or medicines for these illnesses can affect the heart's growth. Other illnesses or medicines seem to have no effect on the baby's heart. Always talk to your healthcare provider for more information.

These things can lead to a higher risk of a birth parent having a child with CHD:

• Seizure disorder and the need to take antiseizure medicines

• Taking lithium to treat depression

• Having phenylketonuria (PKU) and not staying on the special PKU diet during pregnancy

• Insulin-dependent diabetes, especially if blood sugar is not well-controlled

• Lupus

• A connective tissue disorder

• A pregnancy from assisted reproductive technology (ART)

Counseling is important for people with chronic illnesses before becoming pregnant. Always talk with your healthcare provider before taking any medicines while you are pregnant.

Rubella is known to cause birth defects. Rubella is a virus that most people in the U.S. are protected from when they get the measles, mumps, and rubella (MMR) vaccine. A person who has never had rubella or the vaccine should talk with their healthcare provider before becoming pregnant. A person who has rubella during their pregnancy has a very high chance of having a baby with birth defects, including CHD.

Family history and CHDs

About 1 in 100 children are born with a congenital heart defect each year. There is an overall 3 times increased risk for CHD when a first-degree relative has a CHD.

Some heart defects have autosomal-dominant inheritance. This means that with each pregnancy, a parent with the defect has a 1 in 2 chance of having a child with the same heart defect. Males and females are equally affected. There is also a 1 in 2 chance that a baby will not be affected.

People with congenital heart defect should talk with a genetic counselor or genetic specialist before becoming pregnant. In families with CHD in the parents or other children, talk with your healthcare provider about fetal echocardiography. This test can be done in the second trimester, as early as 16 weeks of pregnancy. It looks for major heart defects in the baby.

Chromosome abnormalities and CHDs

Chromosomes are the structures in your cells that contain your genes. Genes contain the code for your traits such as eye color and blood type. Usually, there are 46 chromosomes in each cell of the body. Having too many or too few chromosomes leads to health problems and birth defects. Structural defects of the chromosomes may sometimes occur. This is when a piece of a chromosome is missing. Or it may be duplicated. These also cause health problems.

Problems with chromosomes that lead to genetic syndromes, such as Down syndrome, often result in a higher risk of heart problems in babies. In babies with chromosome abnormalities, around 3 in 10 will have a heart defect.

There are a number of chromosome problems linked with CHD. Some of these include:

• Down syndrome (trisomy 21)

• Trisomy 18 and trisomy 13

• Williams syndrome

• Turner syndrome

• Cri-du-chat syndrome

• Wolf-Hirschhorn syndrome

• DiGeorge syndrome (22q11)

A chromosome analysis can be done from a small blood sample. The test looks for a chromosome problem in a child with a CHD. This can show if chromosomes caused the problem.

Single gene defects

There are about 70,000 genes on the 46 chromosomes in each cell of the body. Genes come in pairs. In each pair, one gene is inherited from one parent, and the other from the other parent. Genes help to control our traits. And they also may cause health problems due to changes in the gene (mutations). When a single gene is changed, a number of health problems may occur. When several health problems occur from one genetic cause, it’s called a syndrome. Some of the genetic syndromes that have a higher rate of heart defects include:

• Marfan syndrome

• Smith-Lemli-Opitz syndrome

• Ellis-van Creveld syndrome

• Holt-Oram syndrome

• Noonan syndrome

• Mucopolysaccharidoses

• Alagille syndrome

Other genetic syndromes that are not due to a single gene defect, but are linked with CHD. These include:

• Goldenhar syndrome (hemifacial microsomia)

• CHARGE syndrome

• VACTERL association

When a child is born with a CHD and may have a genetic syndrome, a healthcare provider who specializes in genetics (clinical geneticist) may be asked to examine and test your child.

If a child has been diagnosed with a chromosomal or other genetic problem, talk with a genetic counselor to help determine the risk for heart defects in future children.