A non-stress test monitors the baby’s heart rate. It is commonly done in the third trimester to check on the fetal health. During this test, the fetal heart rate is monitored to see how it responds both to periods of activity and periods of rest. The physician also watches for uterine contractions. It is called “non-stress” because nothing is done to place stress on the fetus during the test. An obstetrician or MFM reviews the test results.
It’s natural to worry about what caused your child to have CHD. In many cases, there is no clear cause. In some children the heart is the only part of their body that didn’t form normally – this is called an “isolated” abnormality. In other children, CHD occurs with other anatomic differences – this is called “syndromic” abnormality.
There is frequently a genetic component to a cardiac malformation. Genes are often referred to as the “blueprints” for the body and they come packaged in structures called chromosomes. Humans usually have 23 pairs of chromosomes. The genes in our chromosomes are responsible for telling our early embryonic cells how to grow, divide, and eventually form a human body.
Sometimes the fetal genetic information has errors that can result in a problem with the baby’s development. For example:
- There can be an entire extra chromosome = a trisomy
- A piece of a chromosome may be missing = a deletion
- A section of a chromosome can have an extra copy = a duplication
- An error within a single gene that impairs how the protein will function = a pathogenic variant
Chromosomal and genetic testing looks for these mistakes in the genes. A common cause for isolated CHD is a combination of many factors – such as small errors in multiple genes in conjunction with unknown environmental factors (known as multifactorial inheritance).
There are two basic types of genetic tests available in pregnancy: screening tests and diagnostic tests.
Even the most thorough genetic testing may not answer what caused the heart to form abnormally. That’s because scientists don’t know what all the possible mistakes are that can cause cardiac malformations.