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    Prenatal Genetic Testing: Who May Need It and Why

    Updated 24 April 2020 |
    Published 14 October 2019
    Fact Checked
    Tanya Tantry, MD
    Reviewed by Tanya Tantry, MD, Obstetrician & Gynecologist, Medical Consultant at Flo
    Flo Fact-Checking Standards

    Every piece of content at Flo Health adheres to the highest editorial standards for language, style, and medical accuracy. To learn what we do to deliver the best health and lifestyle insights to you, check out our content review principles.

    Many parents worry about whether their unborn child may have genetic conditions that can affect their long-term health or even the infant’s ability to survive after birth. The process of prenatal genetic testing can determine whether a fetus has certain medical conditions while in utero. We’ve put together a guide that can help you better understand genetic testing.

    What is prenatal genetic testing?

    Genetic testing in pregnancy shows the likelihood that an unborn child will have certain inherited health conditions. Genetic testing can also determine, with as much certainty as possible, whether an unborn child has certain genetic disorders or birth defects. These prenatal tests can inform expectant parents about the health of the fetus so they can make informed choices. 

    The tests can also help your health care provider tailor their care for you and increase your chances for a healthy pregnancy.

    Prenatal screening isn’t mandatory — it’s optional. And it’s very important to make an informed decision about whether or not to undergo screening.

    Pros and cons of prenatal genetic screening

    Not all genetic testing has to be done during pregnancy. If two partners both belong to an ethnic group with a higher risk of certain genetic disorders, then the couple may undergo a test to see if they carry certain genes. This is called a carrier screening. Many genetic conditions such as Tay-Sachs, sickle cell disease, and cystic fibrosis require that both parents be carriers of the gene or genes.

    This information can affect family planning choices, including whether to have children or to undergo IVF with preimplantation genetic screening.

    Couples who discover that their baby has a genetic defect are generally referred to a genetic counselor to help them understand the condition and their options.

    Genetic screening in pregnancy can determine the risk for birth defects and genetic conditions, but an actual diagnostic test can tell for sure. Couples who discover that their baby has a genetic defect are generally referred to a genetic counselor to help them understand the condition and their options.

    Types of prenatal genetic testing

    There are a couple of different types of genetic tests that are conducted during pregnancy.

    Screening tests

    Screening tests will determine whether the fetus has a high risk for a certain condition. Here are a few types of screenings:

    • First trimester combined screening is usually performed between weeks 10 and 13 of pregnancy. First trimester combined screenings include ultrasound (nuchal translucency ultrasound measurements) and maternal blood test for PAPP-A and beta-hCG. The results of the blood test, ultrasound, maternal age, and gestational age of the fetus are then used to calculate the risk of genetic disorders like Down Syndrome (trisomy 21), Edwards syndrome (trisomy 18), and Patau syndrome (trisomy 13). 
    • Second trimester screening is performed between weeks 15 and 25 of pregnancy and includes a maternal blood test (a quad test or triple test depending on which state you live in) and ultrasound. The International Society of Ultrasound in Obstetrics and Gynecology recommends performing an ultrasound between 18–22 weeks of pregnancy as part of routine prenatal care. Ultrasound at this point in the pregnancy can detect neural tube defects, anencephaly, congenital heart defects, renal agenesis, gastrointestinal defects, and other conditions. 
    • Modified Sequential Screening is a combination of the first trimester and second trimester screening. The results are first reported after the first trimester sample has been submitted, and a final determination is made after the second trimester sample. Sequential screening has a higher detection rate than individual screen results.
    • Cell-free DNA screening may be performed from 10 weeks on through pregnancy. The test measures small fragments of fetal DNA in the mother's blood and can determine the chance of a chromosomal problem. This test is not recommended for those pregnant with multiples.

    Diagnostic tests

    Diagnostic tests check for the presence of certain genetic conditions, unlike a risk-assessment screen. They’re invasive tests and can diagnose certain fetal conditions with a high degree of accuracy. 

    Diagnostic tests check for the presence of certain genetic conditions, unlike a risk-assessment screen.

    These are some common diagnostic tests:

    • Amniocentesis is usually performed between 15 and 20 weeks of pregnancy. A thin needle is inserted into the womb, and a small amount of the amniotic fluid that surrounds the fetus is removed under ultrasound surveillance. The fluid is then tested for genetic birth defects and abnormal chromosomes. This can also be used as a paternity test while pregnant. Leakage of amniotic fluid and slight bleeding can occur after amniocentesis, but in most cases it stops on its own. There is a very small chance of pregnancy loss because of amniocentesis  
    • Chorionic Villus Sampling (CVS) testing is conducted using a sample of the placental tissue. This test can be performed between 10 and 13 weeks of pregnancy, which is one advantage it has over amniocentesis. However, there is a higher risk of pregnancy loss with CVS.

    You may choose to have fetal genetic diagnostic testing done after your initial screening. Many parents choose to do so if the initial screening detects a higher risk of any abnormalities. Diagnostic testing is more comprehensive than screening and can detect, with as much certainty as possible, conditions caused by an extra chromosome or health conditions that result from missing or damaged chromosomes.

    Many parents choose to have fetal genetic diagnostic testing done if the initial screening detects a higher risk of any abnormalities.