Why does CHD happen?

There are many reasons why the heart of a baby may develop abnormally while in the womb. Here are some examples:

1. Illness during pregnancy - Sometimes, heard defects occur because the mother gets sick. Rubella, also called German measles, is an example of a virus known to cause a specific type of CHD (pulmonary stenosis or narrowing of the pulmonary valve) in the fetus if a mother catches it during pregnancy. Luckily, most people receive the vaccine against rubella for this very reason - to protect the hearts of unborn babies! Other conditions, such as diabetes (high blood sugar) in the mother, can also cause heart defects in the fetus.

2. Vitamin deficiency during pregnancy - If there are not enough of the building blocks necessary for the heart to develop, problems can develop. One example of an important building block is folate, also known as folic acid. This vitamin is important not just for the heart but also for the spinal cord. Babies born to mothers with folic acid deficiency can have CHD (most often problems affecting the highways that leaves the heart to travel to the lungs) as well as a condition called spina bifida. All women of child-bearing age should make sure they are getting enough enough folate in their diet. A multivitamin will usually do the trick. Because the heart develops so early in pregnancy (formation is near complete by around 10 weeks!) problems can happen before a mother even knows she is pregnant.

3. The mother comes in contact with something bad during pregnancy - Smoking is known to cause CHD. Other types of pollution or chemicals that can be breathed or eaten can also cause heart problems in babies. Some medications, such as pills to control seizures, are also known to cause heart defects.

3. Genetics - Some heart problems happen because the instructions on how to build the heart are faulty. These instructions are found in the genes passed down from parents to child.  If a mother or a father - or a sibling, uncle, grandparent etc. - has a heart problem, the chance of a baby having a heart problem is increased. Sometimes doctors can perform a test to find the exact problem in the genes and test for that problem in family members (including unborn babies). Sometimes doctors do not know what the exact problem is and/or no test is available. An example of a genetic problem that can cause heart defects is Trisomy 21 - or Downs Syndrome (when a person has an extra copy of chromosome 21). Half of all babies born with Downs Syndrome have heart problems. It is also important to know that some genetic problems happen during the process of creating a baby - meaning the problems are not present in the parents or other family members. Think of a recipe to make cookies that gets ripped as it is passed from one person to another and the key ingredient of flour is no longer readable. These types of genetic problems are called 'de novo' meaning NEW.

4. Multifactorial - this is a fancy doctor word meaning 'many factors'. Most often doctors do not know why CHD happens. No one in the family has a heart problem. The mother is healthy and did everything right during pregnancy, yet still a baby is born with an abnormal heart. Scientists and doctors are working hard to find out what these unknown causes could be and what can be done to prevent heart problems in babies.