Overview

Congenital heart disease (CHD) refers to a range of defects affecting the normal development of the heart. The term “congenital” means these heart defects are present from birth. CHD often involves changes to the heart’s structure which prevent normal heart function and blood flow through the heart and to the rest of the body. Common heart defects include a hole in the heart wall and problems with the blood vessels or heart valves.

CHD varies from moderate to severe defects, with more complex defects resulting in life-threatening complications. Nevertheless, advancements in diagnosis and treatments have allowed babies and adults with CHD to have improved quality of life and survival. While the exact cause of CHD is still unclear, research has highlighted multiple genetic and environmental risk factors that may increase your likelihood of giving birth to a child with CHD. Understanding these risk factors is fundamental to enabling early detection and intervention. In this article, we will explore the various factors that may contribute to the onset of CHD.

Understanding CHD

What are the different types of CHD?

There are multiple types of congenital heart defects. These defects range in severity from mild to more critical types and can affect different parts of the heart’s structure. The most common kinds of defects include:

Septal defects

Septal defects occur where there is a hole or abnormality in the septum (the wall that separates the heart chambers).

Heart valve defects

Valves are important for regulating blood flow through the heart. Defects in these valves will mean there are problems with blood flow control.

Blood vessel defects

Defects can occur in the large blood vessels that carry blood in and out of the heart. Issues may include blood flowing too slowly, to the wrong place, or in the wrong direction.

Cyanotic vs acyanotic CHD

CHD can be further divided into 2 main groups: cyanotic CHD and acyanotic CHD.

Cyanotic defects are more complex and can cause life-threatening symptoms, requiring immediate treatment. In this type of CHD, babies have more critical defects which reduces the amount of oxygen in the blood. As the blood becomes less oxygenated, this results in cyanosis (blue/grey skin or lips). For those born with cyanotic CHD, surgery is required within the first year of life. An example of a cyanotic defect is the Tetralogy of Fallot. As the name suggests, this particular condition is made up of four defects. The defects that comprise this condition are:

• A large ventricular septal defect (a hole between the left and right ventricles)
• Pulmonary valve stenosis (the pulmonary valves are narrower)
• Right ventricular hypertrophy (the muscle of the right ventricle is thicker)
• An overriding aorta (the aorta is in the wrong position)

Further information about cyanotic CHD can be found here. 

Acyanotic defects differ from cyanotic CHD as they don’t normally interfere with the amount of oxygen in the blood supply. In this type of CHD, you can retain normal/acceptable blood oxygen levels, however, the way blood is pumped around the body remains abnormal. Overall, these defects are often less critical than cyanotic defects and can be corrected during childhood. If the defect persists into adulthood, it does not usually require treatment if you are asymptomatic.

However, more severe cases may require surgery, a cardiac catheter procedure, or medications to help heart function. Babies with mild defects may also be asymptomatic and cyanosis is less common. Examples of acyanotic heart defects include:  

• Atrial and ventricular septal defects (holes in the heart walls)
• Patent ductus arteriosus (the connection between the aorta and pulmonary artery does not close)
• Pulmonary valve stenosis (narrowing of pulmonary valves)

What are the risk factors for CHD?

The exact underlying cause of CHD remains unclear. However, research has shown various genetic, lifestyle and environmental factors may increase your risk of having the condition. 

Genetic conditions

Although in most cases there is no obvious cause of CHD, genetic links for this condition have been identified. Some types of CHD are heritable (i.e., the disease runs in the family) and multiple genetic health conditions have been shown to increase your risk of having CHD.

Genetic conditions associated with CHD include:

Down’s syndrome

Approximately half of all children with Down’s syndrome are reported to have CHD. The most common CHD is a septal defect. This is said to be a result of genetic abnormality which also leads to other disabilities in children with Down’s syndrome.¹

Turner syndrome

This genetic condition only affects females assigned at birth. The heart defect typically associated with Turner syndrome is the narrowing of the valve or artery.²

Noonan syndrome

Noonan syndrome is known to cause a range of symptoms and disabilities, including pulmonary valve stenosis.³

Maternal diabetes

If the mother has diabetes, they have a higher risk of giving birth to a baby with CHD compared to those without diabetes. However, this risk is only increased for those with type 1 diabetes and type 2 diabetes. This doesn’t apply to those with gestational diabetes (a type of diabetes that develops during pregnancy but usually goes away following childbirth). 

The increased risk is said to be caused by the higher insulin levels found in the blood of those with diabetes. The higher insulin levels will disrupt the development of a foetus, thereby resulting in CHD.

Alcohol

Excessive alcohol intake during pregnancy can lead to foetal alcohol spectrum disorder (FASD). This is due to alcohol’s toxicity/poisonous effect on the foetus tissue. Potential congenital heart defects associated with alcohol consumption may include atrial or ventricular septal defects.⁴ 

Smoking

Smoking or secondhand maternal and paternal exposure to tobacco smoke is associated with an increased risk of CHD in offspring.^5,6 

Rubella

Rubella (also known as German measles) is a rare viral infection. For most people, this disease is usually mild and they will recover within a week. But for mothers who become infected during pregnancy, rubella can cause serious problems for unborn babies, especially if the infection occurs in the first 8 to 10 weeks of pregnancy.⁷

To prevent this, the rubella vaccine is offered as part of the NHS’ vaccination schedule. You should contact your GP if you’re unsure whether you have received the vaccine.

Flu 

Contracting flu (influenza) within the first trimester (3 months) of pregnancy increases your risk of having a baby with CHD. The flu vaccine is recommended for pregnant women to help prevent this.

Medicines

Certain medications can increase the likelihood of having a baby with CHD. This includes:

• Some anti-seizure medicines (e.g., benzodiazepines)
• Some acne medicines (e.g., isotretinoin and topical retinoids)
• Angiotensin-converting enzyme (ACE) inhibitors (used for hypertension/high blood pressure)
• Ibuprofen - if you are 30 or more weeks (7 months or more) pregnant and taking ibuprofen, you have an increased risk of giving birth to a baby with CHD

Paracetamol is recommended as an alternative to ibuprofen during pregnancy. However, avoiding taking any medicines, especially during the first trimester, is generally better as there may be adverse consequences. 

Always consult your healthcare provider for more guidance on which medicines are safe to use.

Phenylketonuria 

Phenylketonuria (PKU) is a rare inherited disorder that causes an increase in levels of phenylalanine in your blood. Phenylalanine is an amino acid (a protein building block) which is obtained from eating foods high in protein. People with PKU have high levels of phenylalanine due to a genetic mutation in the enzyme responsible for its breakdown and removal from your body. This results in a harmful buildup of phenylalanine within the blood and brain, leading to brain damage, and learning and behavioural problems. 

PKU is managed by adopting a low-protein diet to limit the phenylalanine intake. A PKU diet avoids high-protein foods such as:

• Meat and fish
• Eggs
• Nuts and seeds
• Dairy (e.g., milk and cheese)
• Soya, Quorn, and tofu
• Flour-based foods (e.g., bread, pasta, cakes, and biscuits) 

Pregnant mothers with PKU who don’t follow this diet are more likely to give birth to a child with CHD, as exposure to high phenylalanine levels is dangerous to the unborn baby.^8,9   

During and before pregnancy, mothers with PKU are recommended to plan their pregnancies by monitoring their blood. Ideally, you should try to conceive when your phenylalanine levels are controlled and within the target range (below 300 µmol/L).

Organic solvents

Organic solvents are chemicals used in a variety of industries and products. For example, they may be found in:¹⁰ 

• Paints
• Varnishes
• Adhesives
• Glues
• Plastics 
• Nail polish 

Organic solvents that have been classified as reproductive hazards are:

• 2-ethoxyethanol
• 2-methoxyethanol
• Methyl chloride  

Some organic solvents are also known to be carcinogens and neurotoxins. Due to their high volatility (ability to evaporate), exposure to these substances is common via inhalation. 

Summary

Understanding the risk factors linked to CHD is vital for both expectant parents and healthcare providers. CHD is one of the most common birth defects, affecting 1 in 100 babies every year. Although most cases of CHD do not have an identifiable cause, there is significant evidence to show various genetic and environmental factors can increase the risk of CHD. This includes genetic conditions like Down’s syndrome and lifestyle factors, such as smoking and alcohol use.

Ultimately, you should attend frequent pre- and antenatal screenings, especially if you have a condition known to increase risk of CHD (such as diabetes or PKU), and consult your healthcare provider to help you identify and manage potential risks during pregnancy. Early detection and intervention of CHD enables babies born with CHD to live longer and healthier lives.