Congenital heart disease - Causes of congenital heart disease

Congenital heart disease is caused when something disrupts the normal development of the heart.

It's thought most cases of congenital heart disease occur when something affects the heart's development during about week five of pregnancy. This is when the heart is developing from a simple tube-like structure into a shape more like a fully developed heart.

While some things are known to increase the risk of congenital heart disease, no obvious cause is identified in most cases.

Increased risk

There are a number of things that can increase the chances of a child having congenital heart disease. Some of these are described below.

See types of congenital heart disease for more information about the different heart defects mentioned below. 

Genetic conditions

Several genetic health conditions that 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 to 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.

Alcohol

If a pregnant woman drinks too much alcohol during pregnancy, it can have a poisonous effect on the tissue of the foetus. This is known as foetal alcohol syndrome.

It is estimated that as many as half of all children with foetal alcohol syndrome will have congenital heart disease, most commonly ventricular or atrial septal defects.

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 to 10 weeks of pregnancy.

A rubella infection can cause multiple birth defects, including congenital heart disease. All women of childbearing 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 against 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.

The flu vaccine is recommended for all pregnant women.

Medications

There are several medications linked to an increased risk of a baby being born with congenital heart disease. These include:

• certain anti-seizure medications, such as benzodiazepines and lithium
• certain acne medications, such as isotretinoin and topical retinoids (see treating acne for more information)
• 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.

Speak to your GP or pharmacist if you are unsure which medications should be avoided during pregnancy.

Phenylketonuria (PKU)

Phenylketonuria (PKU) is a rare genetic condition 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 with PKU who do not do this are six times more likely to give birth to a baby with congenital heart disease than the general population.

Organic 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 paint, nail polish and glue.