Navigating Genetic Testing In Pregnancy
There are so many blood draws, appointments, test results, etc. that make it difficult to keep up and informed. This page serves to discuss some of the tests offered in pregnancy. These tests are optional, and no one has to have these evaluations.
Screening/Blood Tests Available
The goal of a “screen” is to identify if a pregnancy has an increased chance for a chromosomal condition such as Down Syndrome. Every person has the chance to have a baby with a chromosomal condition. Some chromosomal conditions result in an early miscarriage. Other times, a baby may be born with a chromosomal condition that can cause certain features like intellectual disability or a heart defect. There are many interventions and surgeries that can help support a baby with a chromosomal condition.
The specific screen that is offered depends on multiple factors such as a provider’s preferences, patient age, insurance coverage, chance for chromosomal conditions, and accessibility.
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The First Trimester Screen is available in the first trimester around 10 weeks-13 weeks and 6 days of pregnancy. The screen assesses the chance for Down syndrome and Trisomy 18. It is performed via a blood draw. Within the blood, there are two hormones assessed: Pregnancy Associated Plasma Protein-A (PAPP-A) and human chorionic gonadotropin (hCG).
The screen can also use two ultrasound measurements: the absence or presence of the baby’s nasal bone and nuchal translucency (NT). The NT measurement is measuring the amount of fluid that is behind the baby’s neck.
After the hormones and ultrasound measurements are integrated and analyzed, then the chance the pregnancy could have Down syndrome or Trisomy 18 is provided.
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The Quad screen is available after 15 weeks until 22 weeks and 6 days. The quad screen assesses four hormones called hCG, inhibin-A, estriol, and alpha fetoprotein (AFP) which are mostly produced by the placenta during pregnancy. Down syndrome, Trisomy 18, and open neural tube defect risk is assessed with this test.
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These tests require two blood draws: one during the first trimester and another in the second trimester. When the results are available will depend on the specific type of two part screen that was performed. There are primarily three types: Sequential Screen, Combined Screen, and the Integrated Screen. Ultimately, these screens assess the risk for Down syndrome, Trisomy 18, and Neural Tube Defects like the Quad screen but usually with a higher detection rate.
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This screen assesses for the risk for open neural tube defects (ONTD) like spina bifida. This is usually done when someone has completed the first trimester screen or cell-free DNA screen. It does not need to be performed if the Quad screen or a Two Part screen has been completed because those screens already assessed for ONTD.
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Cell-free DNA screening is performed after 10 weeks of pregnancy. It can assess for the chance for Down syndrome, Trisomy 18, Trisomy 13, and sex chromosomal conditions like Turner syndrome or Klinefelter syndrome as well as select microdeletions. Placental DNA in the pregnant person’s blood is analyzed to assess the risk for these conditions.
Diagnostic Testing/Procedures Available
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CVS is a procedure performed after the 10th week of pregnancy until 13 weeks and 6 days. A biopsy of the placenta, specifically the chorionic villi, is sent to a lab to be tested for chromosomal conditions or molecular conditions (like sickle cell disease or cystic fibrosis). The placental biopsy can be obtained either through the cervix or through the abdomen. Ultrasound guidance is used throughout the procedure. There is risk for miscarriage, bleeding, infection, etc. It is important to ask the physician performing this procedure what he or she personally quotes.
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Amniocentesis is a procedure performed after the 16th week of pregnancy. Amniotic fluid is obtained with a long, thin needle entering through the abdomen into the amniotic sac. Ultrasound guidance is used throughout the procedure to get a pocket of fluid away from the baby. The fluid is sent to a lab to be tested for chromosomal conditions or molecular conditions (like sickle cell disease or cystic fibrosis). There is risk for miscarriage, bleeding, infection, etc. It is important to ask the physician performing this procedure what he or she personally quotes.
The above screens assess the chance whereas diagnostic tests provide a yes or no answer whether the pregnancy has the chromosomal condition or other conditions of interest.
Ultrasounds Available
Ultrasound is helpful to diagnose or strongly suggest birth defects like a heart defect or clubfoot. Ultrasound uses sound waves to create images of the baby within the womb. There is a 3-5% chance for a birth difference (check out https://www.cdc.gov/ncbddd/birthdefects/types.html to learn more about the types of birth differences) for any pregnancy; therefore, ultrasound is typically performed in both the first and second trimester to assess for any differences.
Ultrasound can also provide additional context to screening results. For example, if someone had a positive blood test for Trisomy 18 and their ultrasound revealed a heart defect, then there is even more suggestion for the condition. Still, ultrasound cannot diagnosis chromosomal conditions, and it can have limitations.
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The first trimester ultrasound is usually not a comprehensive evaluation of the baby. Some of the main measurements and checks are the amount of amniotic fluid, the growth of the baby, the absence or presence of a nasal bone, and nuchal translucency.
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The second trimester ultrasound is historically the time in which the predicted sex of the baby is revealed. If cell-free DNA screening has been performed, then this ultrasound can help confirm the predicted sex (most of the time!). This ultrasound can usually help to identify if there are any birth differences. Generally, this ultrasound is performed 18-22 weeks of pregnancy.
Carrier Screening Available
Carrier screening is a blood test that looks to see if someone carries a genetic condition that they could pass on to their children. Carriers usually do not have any signs of that condition or have a family history, so they never know they are a carrier until they do the testing. If both members of a couple are carriers of the same condition, then each time they get pregnant, there is a 25% chance their child would have that genetic condition. There are some conditions that are sex-dependent because the genes are located on the X-chromosome. If a woman or person with two X chromosomes is a carrier of the condition, then for each son that is conceived, he would have a 50% chance to inherit the condition. However, sometimes girls can have symptoms of the x-linked condition and are not “just carriers”.
There are many conditions that can be tested for through carrier screening. The features, treatment, lifespan, and risk can all vary depending on the condition. Check out this page for a more detailed discuss on carrier screening.
The above are the most common tests around, but there are a few others:
There is still discussion of the accuracy and utility of these tests. They are not yet recommended by professional organizations. For a refresher on inheritance patterns, please check out this post.
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This blood test has two parts - the first is to evaluate the pregnant person carrier status for select conditions. if they are positive, then the tests evaluates the placental DNA in the pregnant person’s bloodstream to determine in the pregnancy is at a higher risk to have the condition that the patient is a carrier of.
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There is a blood test that evaluates the placental DNA in the pregnant person to determine if there is an increased or decreased chance the pregnancy has certain autosomal dominant conditions. Some of the conditions include achondroplasia, Noonan syndrome, and skeletal dysplasia. Someone may be offered this screen if there are ultrasound findings consistent with one of these conditions and the person does not want to proceed with a diagnostic procedure like an amniocentesis.
Why would someone want to have these tests?
If someone is interested in knowing if there pregnancy has a genetic condition or birth difference, then the above screens and tests may be a good fit. People can use this information for a number of reasons. There has been the view that genetic testing is only for individuals that would consider termination of pregnancy. Some of the above genetic conditions come with challenges, and someone may feel that the challenges are not something they can take on at that time. It is not a light decision. Organizations are available to help people through this time: https://endingawantedpregnancy.com/ and http://www.aheartbreakingchoice.com/.
While termination is one option that someone always has, this is not the only reason someone may proceed with genetic testing. For some, this information can help with their birth plan. They may need to deliver their baby at another hospital to ensure immediate and proper care. Not all hospitals are equipped with the needed machines or staff to care for a newborn with health complications. While still pregnant, there can be appointments with specialists to learn more about conditions and treatment as opposed to waiting until after birth when things may become more hectic. Some treatments are most helpful when they are administered right after birth such as a treatment for spinal muscular atrophy. Waiting for test results after birth may delay treatment.
Individuals may choose adoption as a result of the genetic testing. There are organizations that specialize in adoption for certain genetic conditions such as the National Down Syndrome Adoption Network.
Reassurance is important as well. Someone may know they are a carrier of a certain condition and want to know while pregnant if it was passed down. Not all genetic results are positive - many times the results are negative and for some, they need that information to feel more relaxed throughout their pregnancy as opposed to feeling anxious the entire time.
Some people choose not to have the above testing. They may feel that the information wouldn’t change anything for them and are comfortable waiting until the baby is born to determine if genetic testing is needed. Most babies are not born with genetic conditions.
There is no one size fits all approach when it comes to genetic testing. Some individuals want as much accurate information whereas other individuals are more open to letting things be. There are some clinics where genetic testing is thought of as routine. It is important to discuss with your healthcare provider what tests, if any, you are open to having done.
Where can I learn more about some of the conditions that can be assessed?
Spinal Muscular Atrophy
Spinal Muscular Atrophy (SMA) is now identified at higher frequencies than in the past given it is recommended to be offered as a part of routine carrier screening to all patients. CureSMA.org goes into more detail of the features of SMA as well as the new drug therapies which have been shown to delay symptoms and increase lifespan when administered early in life.
Hemoglobinopathies
Hemoglobinopathies may be the most common genetic conditions. It is important to determine the exact hemoglobinopathy that has been diagnosed and discuss the features of that particular hemoglobinopathy. Sickle Cell Disease and a Sickle Cell Center of Excellence can be great resources to learn more.
Cystic Fibrosis (CF)
Cystic Fibrosis Foundation has a great introduction to the condition and links to research.
Trisomy 13 and Trisomy 18
Often Trisomy 13 and Trisomy 18 are discussed together; however, the conditions are substantially different in their features and life expectancy. Trisomy.org is an excellent resource and makes available factual pamphlets for individuals to learn more about each condition.
Down Syndrome/Trisomy 21
Every state, and sometimes cities, will have a Down Syndrome Network or Association for support. DownSyndromePregnancy.org is a great resource as well as the American Academy of Pediatrics.
Sex Chromosomal Differences
Triple X syndrome, Klinefelter syndrome, XYY syndrome, and other variations of sex chromosome difference can now be screened for with cfDNA screening. The AXYS Association is a great network of support and resources. Living with XXY is another helpful organization for Klinefelter syndrome.
Turner Syndrome
Turner syndrome is when there is one X chromosome as opposed to two. It is considered a sex chromosomal difference. The Turner Syndrome Society provides excellent resources.
Blog Posts
Heath care providers such as genetic counselors can further discuss the above testing and screening options. Check out: Find a Genetic Counselor.
Resources:
"Practice Bulletin No. 162: Prenatal Diagnostic Testing for Genetic Disorders" Obstet Gynecol. 2016 May;127(5):e108-e122. doi: 10.1097/AOG.0000000000001405.
American College of Obstetricians and Gynecologists’ Committee on Practice Bulletins—Obstetrics et al. “Screening for Fetal Chromosomal Abnormalities: ACOG Practice Bulletin, Number 226.” Obstetrics and gynecology vol. 136,4 (2020): e48-e69. doi:10.1097/AOG.0000000000004084