85-90% of cases of CHD have no known cause or origin. In these cases the cause is theorized to be a form of multifactorial inheritance. This means that a possible combination of genetics from both parents and unknown environmental factors are involved in causing the heart defect.

Approximately 5% of CHDs are caused by chromosomal abnormalities. Normally a child inherits 23 chromosomes from each parent for a total of 46. Having extra chromosomes or too few chromosomes can result in birth defects like CHD. A few chromosomal abnormalities associated with CHD are:

• Down Syndrome (Trisomy 21) – approximately 50% of babies born with Down Syndrome also have a congenital heart defect. The most common CHDs associated with Down Syndrome are Aterioventricular Septal Defects (AVSD), septal defects (ASD and/or VSD), and patent ductus arteriorsus (PDA).
• Trisomy 18 and Trisomy 13
• DiGeorge Syndrome (22q11.2 deletion)
• Wolf-Hirshhorn Syndrome
• Turner’s Syndrome and Mosaic Turner’s Syndrome
• Cri-du-chat Syndrome

3-5% are due to single gene defects. The 46 chromosomes found in each cell are comprised of approximately 70,000 genes. Genes come in pairs with one gene inherited from the mother and one from the father. When a gene is abnormal (mutated) a number of health problems can arise, such as CHD in some cases. When a single gene mutation causes a set of health problems it is referred to as a syndrome. Some of the genetic syndromes associated with CHD are:

• Noonan Syndrome
• Marfan Syndrome
• Holt-Oram Syndrome
• Costello Syndrome
• CHARGE Syndrome

2% can be attributed to environmental factors. Many mothers may be initially tempted to blame themselves for their baby’s CHD diagnosis thinking they did something wrong during pregnancy. It’s important to remember that most cases of CHD have no known cause and are not the result of anything you did or didn’t do. However, there are some medications and health conditions that are known to cause an increased risk in the occurrence of CHD, especially during the first few weeks of pregnancy when the heart is developing. Some known environmental risk factors are:

• Some anti-seizure medications
• Lithium based anti-depressants
• Insulin-dependent diabetes (especially if not well controlled)
• Lupus
• Rubella (during pregnancy)

Talk to your OB about your medications and any risk factors you may have before becoming pregnant or as early in your pregnancy as possible.

If you are a parent with CHD your risk of having a child with CHD is increased compared to the general population. Talk to your doctor about if your heart defect could be genetic and what prenatal testing would be recommended.

If you are a parent of a child with CHD you may be wondering what your risk of having a second child with CHD is. For most healthy parents the rate of having a heart healthy child is 99%. When you have a child with CHD the risk of having a second child with a heart defect is increased by only 2-3%.