Sara contacted us on the MotherToBaby live chat service after being referred by her OB/GYN, who told her that the Paxil (drug name paroxetine) she was taking could cause a heart defect. She was 14 weeks old and wanted to learn more, but she was confused because all her genetic test results had come back normal. She asked: “How could my baby have a heart defect if my NIPT was negative?”
During pregnancy, many tests are done to check your baby’s health and development. It can be hard to keep track of what everyone is searching for and why it’s important. To understand these tests, it can be helpful to know the differences between a genetic deficiency and a chromosomal abnormality and what each means for your baby’s health.
All pregnancies have a historical risk of birth defects of 3-5%, but some exposures may increase the risk of birth defects above this historical estimate. Most birth defects appear during the first trimester, while the baby is growing and developing. A certain part of the body – such as the heart, brain or limbs – may not develop properly, and the baby’s body may look or work differently than it should. You may have heard of a baby being born with a hole in the heart or something called a cleft lip. These are two examples of birth defects that can occur during pregnancy. Birth defects can range from mild to severe, and the baby’s health will depend on where the birth defect occurs and how severe the problem is.
Some tests done during pregnancy can check your baby for birth defects. For example, most pregnant women will have an anatomy scan between 18 and 22 weeks where the healthcare provider will examine the baby using an ultrasound. Most people know by the time they can find out the baby’s sex, but the ultrasound will also look in detail at the baby’s organs and body parts, including the heart, brain, face and stomach, to check for birth defects. . Although this is an important screening test, it is not perfect, and smaller defects may go unnoticed until birth.
Chromosomal abnormalities are changes in the baby’s DNA that occur at the time of conception. The best way to understand DNA is to think of it as a recipe book that contains all the recipes for the growth and development of different parts of the body. If a particular recipe calls for one stick of butter, but the printed book mistakenly says two sticks of butter, the recipe will be different. Likewise, people sometimes have extra or missing amounts of DNA that can cause developmental changes. For example, people who have a chromosomal abnormality known as Down syndrome have three copies of their 21st chromosome rather than just two. It is this extra amount of DNA that causes the developmental differences in people with Down syndrome.
During your pregnancy, your healthcare provider may suggest that you meet with a genetic counselor to have non-invasive prenatal testing, or NIPT. This test can be done as early as 10 weeks. During pregnancy, some of the baby’s DNA enters the pregnant woman’s bloodstream. By taking a small sample of mom’s blood, a lab can take a look at the baby’s DNA and tell if it has certain chromosomal abnormalities, such as Down syndrome. When you meet with a genetic counselor, he or she will review all the pros and cons of this test, as well as your family history, and meet with you again to review the results.
Returning to the live chat service, Sara asked: “Because my NIPT results were normal, the baby is unlikely to have a chromosomal abnormality. However, a birth defect could still have occurred in the first trimester and I have to wait until the anatomical scan to get those results, is that right?’ Exactly, I replied. I then explained that although Paxil (paroxetine) has been shown to increase the risk of heart defects in some studies, other studies suggest no risk, so the overall chance of the baby being affected is low.
As we finished our conversation, Sara shared that she felt much more knowledgeable about the difference between a genetic deficiency and a chromosomal abnormality. She was able to breathe a sigh of relief that her NIPT results came back normal, indicating a low risk for conditions such as Down syndrome. She also felt much more confident going into her anatomy scan in a few weeks knowing that this test, while not perfect, would be the best way to detect birth defects before her baby was born.
If you have any questions about birth defects or exposures during pregnancy, talk to a MotherToBaby specialist by phone, text, live chat or email. For any questions about genetic testing in pregnancy or to find a genetic counselor in your area, visit the Find a Genetic Counselor page on the National Society of Genetic Counselors website:
