Is genetic testing right for you? Understanding the basics of your genetic code.
When you get pregnant, it is a very special and important time. You are bringing a new life into the world. You want your baby to be happy and healthy. As a parent, you know that there are options to investigate the health of your baby, but you might now know what they are or what they mean. If you are interested in finding out, I encourage you to read on.
When a new life is conceived, genetic information from both parents comes together to form the embryo. This genetic information is held in chromosomes; 23 chromosomes come from mom and 23 come from dad. The process by which they arrive in the embryo is a complicated one, and things can go wrong along the way. You may remember back to high school biology when you learned about meiosis, the process by which egg and sperm cells are made. In this process, there are multiple points that the process can go awry, and this has a chance of happening in any egg or sperm. Sometimes an error can occur that results in a disease causing mutation on a chromosome. Sometimes extra or missing chromosomes can end up in the sperm or egg.
The longer you live on this planet, the more you see people affected by disease. Disease can be genetic, or caused by infection, a poor diet, or an unhealthy habit. There are many, many genetic causes of disease. Some are well understood and some are not. Over the past 20 years, extensive research has been carried out into genetic causes of disease that cause developmental disability in children, as these conditions can be lifelong and difficult to treat. The most common causes of developmental disability are genetic. They include Down syndrome and fragile X syndrome.
Although most pregnancies are healthy, all pregnancies are at risk for birth defects and genetic disease. Approximately 2-3% of babies are born with a birth defect. Although there is a risk for genetic disease in any baby, the risk for genetic abnormalities of chromosome number, such as Down syndrome, becomes higher as you age. However, women of any age can have a baby with Down syndrome. People with Down syndrome have an extra chromosome 21. Trisomy 13 or trisomy 18 are other examples of chromosome abnormalities that are more rare, but also more severe than Down syndrome. When you are pregnant, there are multiple tests you can take that tell you about the health of your baby. Your doctor may offer these tests to you. It is up to you to decide if you want to have these tests. Genetic testing can be helpful in pregnancy for several reasons:
Genetic testing can be helpful in pregnancy for several reasons:
1. Normal testing will put your mind at ease
2. If a genetic problem is found, you can learn about it and prepare
3. The information is useful when making decisions about managing the pregnancy
There are two types of testing available in pregnancy: screening and diagnostic testing. Both types of tests have pros and cons. Screening tests give you more information and have no risk. These tests are performed through blood work on a pregnant woman and ultrasound. The problem with screening tests is that they do not detect every abnormal case, they only test for some problems, and they are sometimes inaccurate. Screening tests provide a risk estimate, such as 1 in 5 or 1 in 10,000. If a screening test is abnormal, further diagnostic testing is required to confirm the results. Examples of screening tests include the nuchal translucency screen, the quad or sequential screen and the NIPS test (also called cell free DNA).
When you are pregnant, there are multiple tests you can take that tell you about the health of your baby. Your doctor may offer these tests to you. It is up to you to decide if you want to have these tests.
Diagnostic testing provides a definitive (yes or no) diagnosis. This type of test allows you to test for many more things, including more genetic causes of disease or disability that would be missed by screening tests. Furthermore, they are very accurate. Unfortunately, diagnostic testing requires an invasive procedure. In the first trimester, CVS (chorionic villus sampling) is performed. This test extracts a very small amount of the placenta using a needle which is guided into the placenta across the mothers abdomen using ultrasound. In the second trimester, amniocentesis is performed. During this test, a small amount of fluid from around the baby is removed with a needle under ultrasound guidance. Both of these tests have a small risk for miscarriage of about 0.1-0.5%.
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Victoria Minior, MD
Dr. Minior is a perinatologist (also known as a maternal-fetal medicine specialist), which is an obstetrician/gynecologist with specialized training in obstetric and gynecologic ultrasound and high-risk pregnancies. Her office is located at 30 East 60th Street, Suite 1902, New York, NY 10022.