During the first half of your pregnancy, you and your provider will likely discuss whether or not you would like to move forward with any genetic screening or testing to understand the risk of your little one having any genetic conditions or disorders. Some expecting parents choose not to do any testing, while others may decide to do genetic screening or even prenatal diagnostic testing (such as amniocentesis). But what’s the difference? This blog details the basics of prenatal diagnostic testing, including amniocentesis.
You can read more about prenatal genetic screening here.
What Are Prenatal Diagnostic Tests?
Prenatal diagnostic tests help determine, in a more definitive way, whether your fetus has an abnormal number of chromosomes or an inherited genetic disorder. These tests are more invasive than genetic screening tests, and are done using the cells of the fetus or placenta. These cells are gathered through one of two ways: amniocentesis, or chorionic villus sampling.
Depending on what information or disorder your provider is looking for, the cells can be assessed in a number of different ways using several different technologies. A genetic counselor or provider with genetic expertise will recommend specific tests based on family history or genetic screening and help you understand the results.
What Is the Difference Between Amniocentesis and Chorionic Villus Sampling?
Amniocentesis
Amniocentesis takes a small sample of the amniotic fluid that surrounds the fetus and use the cells present to diagnose chromosomal disorders, neural tube defects, and other genetic defects. Amniocentesis is typically offered between weeks 15-20 of pregnancy, but can be done throughout your pregnancy. It’s important to note that there is a very small risk of pregnancy loss after amniocentesis.
To perform an amniocentesis, the provider will clean your abdomen with antiseptic, apply a local anesthetic to numb the skin, then insert a very long, thin, hollow needle into the abdomen and amniotic sac. This needle allows the provider to withdraw a small sample of the amniotic fluid which contains cells shed by your fetus. Ultrasound technology is used throughout the procedure to help guide the needle into the amniotic sac. When doing amniocentesis for a pregnancy with multiples, a sample must be obtained from each amniotic sac.
After amniocentesis you may feel cramping, notice slight leakage of amniotic fluid, or experience a small amount of bleeding. In many cases, these side effects will stop on their own. It’s important to avoid strenuous activity for 24 hours after this procedure.
Chorionic Villus Sampling (CVS)
Chorionic villus sampling is a prenatal test that obtains cells from the placental tissue to test for chromosomal abnormalities and genetic problems. CVS does not provide diagnostic information on neural tube defects. While CVS can be conducted earlier than amniocentesis (typically between 10 and 13 weeks of pregnancy), there is a slightly higher chance of miscarriage than with amniocentesis.
To perform CVS, a small tube, called a catheter, is inserted through the vagina and into the cervix. Using an ultrasound, the catheter is guided into place near the placenta, and a special syringe at the end removes tissue for testing. You can expect cramping during and after the procedure
What Do the Results of Prenatal Diagnostic Testing Mean?
Many times the results of prenatal diagnostic tests are negative, meaning your little one does not have the condition of concern. It’s important to remember, while a negative test might rule out that specific disorder, there’s always a possibility that the fetus could have another condition not included in the diagnostic test.
If a diagnostic test is positive, your provider or a genetic counselor will explain the results and help give you guidance about the condition, including: life expectancy, treatment options, additional ultrasounds, the care your child will need, and your options for the care of your pregnancy. It’s also important to consider a joining a support group or having a conversation with a counselor or social worker. Having the ability to ask questions and gather information from compassionate and understanding people is unmatched.
Should I Get Prenatal Diagnostic Testing?
Just like genetic screening tests, this is an extremely personal choice and you should work with your partner and provider to weigh your options. It can be good to think about what you would do with the information in the event that the results are positive. Would it give you more time to consider any special care your little one would need? Would it help to know information about life expectancy? Would you make the choice to end the pregnancy? Some parents choose to move forward with prenatal diagnostic tests, and others simply don’t. There’s just no right answer, mama. Use your belief systems and intuition as your guide.