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The basics of congenital heart disease

Congenital means present at birth. So congenital heart disease (CHD)—or congenital heart defects (CHD)—refer to a problem with the heart’s structure that is present at birth. Such defects are not rare; they occur in nearly 1 out of 100 newborn infants.1

Depending on the specific type of disease, blood flow through the heart can be slower than usual, flow in the wrong direction or to the wrong place, or be blocked completely.

There are at least 35 types of congenital heart disease, and we cannot cover all of them here. We will briefly summarize the major types of CHD that are associated with:

  • Heart valves

  • Small holes that allow blood to flow improperly from one heart chamber to another

What causes CHD?

When parents first discover that their baby or child has a heart abnormality, it is common to ask,
“Why has this happened?”
“Will it happen again in our family?”
These same questions come up when a person with congenital heart disease considers having children.

The causes of heart defects.


A congenital heart defect is a heart problem which is present at birth. It is caused by abnormal formation of the heart during fetal development. Congenital heart defects are the most common types of birth defects, affecting 1 in 100 babies. In most cases, when a baby is born with congenital heart disease, there is no known reason for it.

Some of the known causes of congenital heart defects include genes, environmental factors and other factors relating to maternal health. In around 8 out of 10 cases, the reason for the congenital heart defect is unknown.

Most mothers of babies born with congenital heart disease will look critically at their own behaviors during pregnancy to try to find a cause for their child’s illness.

It is important to remember that most cases of congenital heart disease have no known cause. However, some types of congenital heart defects are known to occur more often when the mother comes into contact with certain substances during the first few weeks of pregnancy, while the baby’s heart is developing. Some maternal illnesses and medications taken for these illnesses have been shown to affect the heart’s development. Other illnesses or medications seem to have no impact on the baby’s heart.

Always consult your doctor for more information.

Most cases of congenital heart disease have no known cause. Some of the known causes of congenital heart disease include:

  • Genes – 20 per cent of cases have a genetic cause

  • Other birth defects – a baby affected by certain birth defects, such as Down syndrome, is more likely to have a heart defect

  • Maternal illness – illness of the mother during pregnancy (for example, rubella – now rare) may increase the risk of congenital heart disease

  • Medication and drugs – medication (over-the-counter or prescription) or illicit drugs taken by the mother during pregnancy may increase the risk of congenital heart disease

  • Alcohol – large amounts of alcohol during pregnancy may increase the risk of congenital heart disease

  • Maternal health – factors such as unmanaged diabetes and poor nutrition during pregnancy may increase the risk

The genetics of heart defects

The risk of congenital heart disease increases when either parent has congenital heart disease, or when another sibling was born with congenital heart disease.

If there are no other family members with congenital heart disease, the chance of a congenital heart abnormality in a future pregnancy (brother or sister) is quite small, about 3-4%, as compared to the usual community risk of about 1%.

If we know the chromosomal or gene change that caused the heart defect, it can be easier to predict how likely it is that an abnormality might occur in a brother, sister, offspring or parent of the affected child.

In most cases of congenital heart disease, the cause is unknown and there are limited options for genetic testing.

As children with congenital heart disease enter reproductive age, it is important that they engage in healthy, positive and informed discussions with their parents about the heritable aspects of congenital heart disease, as this could have significant implications for future family planning.

How Can Congenital Heart Disease Be Prevented?

Women who are pregnant or plan on becoming pregnant can take certain precautions to lower their risk of giving birth to a baby with a congenital heart defect:

  • If you’re planning on becoming pregnant, talk to your doctor about any prescription or over-the-counter medications you’re taking.

  • If you have diabetes, make sure your blood sugar levels are under control before becoming pregnant. It’s also important to work with your doctor to manage the disease while pregnant.

  • If you weren’t vaccinated against rubella, or German measles, avoid exposure to the disease and speak with your doctor about prevention options.

  • If you have a family history of congenital heart defects, ask your doctor about genetic screening. Certain genes may contribute to abnormal heart development. 

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