Congenital heart disease is caused when something disrupts the normal development of the heart.
The development of the heart
The development of the heart is a very complex process with several stages. Anything that disrupts this process could cause a type of congenital heart disease to develop.
The main stages of the heart’s development are:
- stage 1 – types of specialised cells come together to form a horseshoe-shaped tube of tissue (this occurs around day 15 of pregnancy)
- stage 2 – the tube grows in size and begins beating (this occurs around day 20 of pregnancy)
- stage 3 – the heart begins to loop and fold in on itself, creating the chambers of the heart. At the same time, blood vessels that connect the heart to the rest of the body are created (this occurs between day 28 and day 32 of pregnancy)
It is thought that most cases of congenital heart disease occur when something disrupts the crucial third stage of the heart’s development.
While some genetic and environmental factors are known to increase the risk of congenital heart disease, in most cases no obvious cause can be found.
Risk factors
Genetic conditions
Several genetic health conditions, which a baby inherits from one or both parents, can cause congenital heart disease.
Down’s syndrome is the most widely known genetic condition that can cause congenital heart disease. Children with Down's syndrome are born with a range of disabilities as the result of a genetic abnormality.
About half of all children with Down’s syndrome have congenital heart disease. In 90% of cases, this is a type of septal defect.
Other genetic conditions associated with congenital heart disease include:
- Turner syndrome – a genetic condition that only affects females. It is estimated that 25% of children with Turner syndrome will be born with congenital heart disease, which is usually a type of obstruction defect.
- Noonan syndrome – a genetic disorder that can cause a wide range of potential symptoms. Around 80% of children with Noonan syndrome will be born with congenital heart disease. In about half of all cases, this will be pulmonary stenosis.
Maternal diabetes
Women with diabetes are five times more likely to give birth to a baby with congenital heart disease than women who do not have diabetes. It is estimated that 3–6% of women with diabetes who become pregnant will give birth to a baby with a heart defect, most commonly transposition of the great arteries.
This increased risk only applies to type 1 diabetes and type 2 diabetes. It does not apply to gestational diabetes, which can develop during pregnancy and usually goes away once the baby is born.
The increased risk is thought to be caused by the high levels of the hormone insulin in the blood, which may interfere with the normal development of a foetus.
Foetal alcohol syndrome
Foetal alcohol syndrome refers to a range of birth defects caused by a child’s mother drinking too much alcohol during pregnancy. Alcohol can have a poisonous effect on the tissue of the foetus.
It is estimated that as many as half of all children with foetal alcohol syndrome will have congenital heart disease, most commonly an atrial septal defect.
The Department of Health recommends that pregnant women should not drink alcohol. If you choose to drink, you should not drink more than one or two units of alcohol once or twice a week, to minimise the risk to your unborn baby.
See Can I drink alcohol if I’m pregnant? for more information about alcohol and pregnancy.
Rubella
Rubella (German measles) is an infectious condition caused by a virus. Rubella is not usually a serious infection for adults or children. However, it can have a devastating effect on an unborn baby if a mother develops a rubella infection during the first 8–10 weeks of pregnancy.
A rubella infection can cause multiple birth defects, including congenital heart disease. All women of child-bearing age should be vaccinated against rubella. The vaccine is now given as part of the routine childhood vaccination schedule. Contact your GP for advice if you're not sure whether you have been vaccinated for rubella.
Flu
Women who get flu during the first trimester (three months) of pregnancy are twice as likely to give birth to a baby with congenital heart disease than the general population. The reasons for this are unclear.
Vaccination for seasonal flu and swine flu is recommended for all pregnant women.
Ibuprofen
Women who take the painkiller ibuprofen during the first trimester of their pregnancy are twice as likely to give birth to a baby with congenital heart disease than the general population.
Paracetamol is a safer alternative, although ideally you should avoid taking any medicines while you are pregnant, particularly during the first three months of pregnancy.
See Can I take ibuprofen when I’m pregnant? and Can I take paracetamol during pregnancy? for more information and advice.
Phenylketonuria (PKU)
Phenylketonuria (PKU) is a rare genetic condition that is present from birth. In PKU, the body cannot break down a chemical called phenylalanine which builds up in the blood and brain. This can cause symptoms such as learning and behavioural difficulties.
PKU can usually be controlled by sticking to a low protein diet. Pregnant mothers who do not do this are six times more likely to give birth to a baby with congenital heart disease than the general population.
Organ solvents
Women who are exposed to organic solvents are three times more likely to give birth to a baby with congenital heart disease than the general population. Organic solvents are chemicals found in a wide range of products and substances, such as:
