What are congenital defects? 

Congenital defects are problems with how the body is formed or how the body works, which happen during the development of the baby in the womb. These defects are observed in the fetus whilst still in the womb, or in early childhood (a few years after birth).

An enlarged heart refers to a condition where either all chambers or sections of an infant's heart are larger than what is considered to be the standard size. This is usually the result of a condition, a problem with the heart structure or function that one is either born with or develops later in life.

An enlarged heart can make your heart either larger and weaker or thicken your heart muscle, and it can be short-term or lifelong, depending on the cause.^1,2 The abnormal structure of the heart chambers, valves, or great vessels in patients with congenital heart disease changes the normal blood flow pattern.³ 

The Centres for Disease Control and Prevention (CDC) reports that a problem with how the heart is formed and how the heart functions is one of the most frequent birth defects worldwide. It contributes greatly to poor health outcomes, and it is also one of the most common and expensive defects to treat. While improvements in diagnosing and treating heart defects have helped people live better lives, many serious heart issues can only be managed, not cured. The best goal is to prevent heart defects before they happen by focusing on factors that can be controlled or changed.⁴

This article will focus on the risk factors of an enlarged heart and what you can reasonably do to prevent an enlarged heart that develops when your baby grows in the womb.

Genetic congenital defects that can cause an enlarged heart

Genetic disorders, environmental factors and a complex interaction of genetic and environmental influences can cause the development of heart defects that can lead to an enlarged heart.⁴ 

Genetic disorders are health issues that arise due to changes (or mutations) in our genes. Genes are like instructions for our body, they tell our cells how to grow, develop, and work. We get our genes from our parents, and most of the time, they work correctly, but sometimes, changes in those instructions can lead to problems. Chromosomes carry genes.

Some chromosomal abnormalities that can cause heart defects resulting in an enlarged heart include: 

• Down syndrome is also known as trisomy 21 (a person has an extra copy of chromosome 21) 
• Edwards syndrome, also known as Trisomy 18 (an extra copy of chromosome 18)
• Patau syndrome, also known as Trisomy 13 (an extra copy of chromosome 13)
• DiGeorge syndrome (some part of chromosome 22 is missing)

Disorders caused by a change in a single gene resulting in an enlarged heart include

• Allagile syndrome
• The Noonan syndrome
• Charge syndrome

Congenital abnormalities of the heart and blood vessels, which develop during fetal growth and are present at birth, can impair their function and lead to an enlarged heart. These defects include: ⁴

• Ventricular septal defects (defect in the hole between the ventricles)
• Atrial septal defects (a defect in the hole separating the atrium)
• Hypoplastic left heart syndrome (a condition where the left side of the heart is severely underdeveloped during fetal development)
• Tetralogy of Fallot (a condition where a baby is born with four different heart defects, that is, ventricular septal defects, narrowing of the pulmonary artery and valve, overriding aorta, and thicker right ventricles) 
• Transposition of the great arteries (a defect where the two main blood vessels that leave  the heart, the aorta and pulmonary artery, are not in their usual positions)
• Ebstein's Anomaly (a condition where the valve that separates the right atrium and ventricle is not well-formed)
• Coarctation of the aorta, also known as narrowing of the aorta (a condition where a part of the aorta is very small) 
• Truncus arteriosus: a condition where the pulmonary artery and aorta fail to separate during development, resulting in the mixing of oxygen-rich and oxygen-poor blood
• Uhl’s anomaly (a rare congenital heart defect associated with partial or complete absence of the right ventricle)⁵

What non-genetic factors increase the possibility of a fetus having an enlarged heart?

The risk of a fetus developing an enlarged heart increases if the mother is exposed to certain medications, recreational drugs, environmental toxins, or harmful paternal factors.

People assigned females at birth during their reproductive years are at risk of having a fetus with an enlarged heart if they:⁶ 

• Do not take prenatal multivitamins, especially folic acid.
• Consume alcohol during pregnancy.
• Have chronic illnesses such as diabetes or phenylketonuria (PKU).
• Have high blood pressure (hypertension).
• Are obese or overweight.
• Have anaemia (a low number of healthy red blood cells).
• Experience physical or emotional abuse.
• Have pre-existing heart conditions.
• Smoke or are exposed to second-hand smoke.
• Are exposed to teratogens (substances that cause birth defects), including:
  • Thalidomide
  • Rubella virus (German measles)
  • Retinoic acid (used in acne medications)
  • Indomethacin is used in tocolysis (to delay labour)

Other causes of heart enlargement in a baby include:⁷ 

• Infection during pregnancy that affects the baby in the womb
• Reduced development of the baby in the womb
• Irregular heartbeat
• The presence of one kidney or the total absence of both kidneys (renal agenesis) 
• Twin-to-twin transfusion syndrome: This is a condition where twins or more babies in the womb share a placenta. This causes uneven blood flow between the babies, potentially affecting the heart and other organs

What preventive measures can be taken to avoid heart enlargement from congenital defects?

One of the most effective ways to prevent heart enlargement from congenital defects for most individuals is to promote and practice preconception care throughout their reproductive years.⁸

What is preconception care?

Preconception care is about taking steps to stay healthy before getting pregnant. It includes medical, lifestyle, and social support for women and their partners to help them be in the best health possible before, during, and between pregnancies. The goal is to make sure the mom stays healthy and has a healthy baby, with the hope that both will stay healthy in the long run. 

Why is it essential to start prevention before getting pregnant? 

It is important for the following reasons:

• The primitive heart tube (a simple tube that will later grow and change into a fully working heart) starts to beat regularly around the 3rd week after fertilisation, and antenatal care and screening typically starts after many weeks and even months from the last menstrual period, and that will be too late to prevent heart abnormalities
• Pregnancies can occur unplanned
• It takes time to achieve proper metabolic control for chronic conditions such as diabetes and phenylketonuria; thus individuals with these chronic conditions need to have them properly managed by a healthcare provider before getting pregnant
• Preconception care helps to detect unrecognised diabetes present before pregnancy

Other factors in preconception care involve

• Taking a daily multivitamin that has folic acid and avoiding high amounts of retinol (>10,000 IU)
• quitting smoking and avoiding being exposed to second-hand smoke
• informing your healthcare provider or obstetrician of prescribed medications you take, such as medications for seizure and depression (paroxetine), and retinoic acid, including over-the-counter medications, to ensure that the medications can be changed or altered accordingly
• Both you and your partner should avoid exposure to dangerous substances/chemicals such as herbicides, pesticides, heavy metals, toluene, xylene, benzene, etc, at home or at your workplace
• avoiding close contact with individuals who are sick, especially those who have an illness that causes a high temperature, and practising good hygiene
• maintaining a healthy weight, being physically active, eating healthy meals (including foods rich in folate) and starting prenatal care as soon as possible

These preventive measures increase the possibility of giving birth to a healthy baby with a normal heart. Hence, starting preconception care helps to minimise the risk of having a baby with an enlarged heart.^4,7

Summary

An enlarged heart is usually a result of problems with the way the heart and its surrounding blood vessels work and is formed when the baby is growing in the womb. Certain factors influence the development of an enlarged heart in a fetus. They include genetic disorders, exposure of the parents to dangerous chemicals, overuse of prescribed and over-the-counter medications, and poor management of chronic health conditions of the mother, such as diabetes and phenylketonuria, before getting pregnant. An enlarged heart may be prevented if the soon-to-be parents get preconception care, avoid exposure to dangerous chemicals and maintain a healthy lifestyle.