fbpx What Parents Should Know About Prenatal Genetic Testing

What Parents Should Know About Prenatal Genetic Testing

Screening and diagnostic tests can help you make informed decisions about your pregnancy.
Britany Robinson
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Britany Robinson

You might imagine the moment you hold your baby to your chest for the first time. You might think ahead to their first words, first steps or first birthday. Maybe you go so far as to wonder what they will look like as an adult; will they have your nose and passion for music or your partner's knack for cooking?

Looking to the future should be exciting. But there are aspects of looking forward that might be stressful or scary, particularly when it comes to your child's health—which will most likely be good! Still, every parent worries about the potential health issues that could affect their child's future. Prenatal genetic testing allows us to rule out or prepare for some of those possibilities.

Prenatal genetic testing refers to screening and diagnostic tests that can be done before or during pregnancy to predict or diagnose certain birth defects or genetic disorders.

Choosing to undergo prenatal genetic testing is a personal and sometimes complicated decision. But it helps to know the details about these options—and why experts might encourage you to consider certain prenatal genetic tests.

Types and timing of prenatal genetic testing
Illustration by Joshua Christensen

Prenatal genetic testing is an option for all future parents either before or during pregnancy. If you or your partner has a history of genetic disorders in your family, or you're 35 or older (which scientists have found increases your risk of having a baby with missing, damaged or extra chromosomes) then your OB-GYN is more likely to refer you to a genetic counselor who can guide you through the options.

Genetic testing can be expensive, but many insurance companies will cover testing for high-risk pregnancies and for women 35 and older. You may need a referral from your doctor in order to get coverage.

The tests you might be presented with fall into two categories: screening tests and diagnostic tests.

Screening tests

The first type of screening test is a carrier screening, which tests the people who are or want to become pregnant, using blood or a tissue sample from inside the cheek. The carrier screening can detect the genes for certain inherited disorders, such as cystic fibrosis, Tay-Sachs disease, sickle cell disease and fragile X syndrome.

If both people who are trying to get pregnant together carry a recessive gene of one of these disorders (or other less common ones), their offspring have a roughly 25 percent chance of inheriting the abnormal gene and a 50 percent chance of becoming a carrier with a recessive gene.

The carrier screening can be done before a person is pregnant, while the next two tests are done during the first trimester. First-trimester screening includes a blood screening of the pregnant person and an ultrasound.

The nuchal translucency test is the first-trimester ultrasound screening, which measures the thickness of skin at the back of the fetus' neck. An increased thickness can be an early indicator of Down syndrome.

Additional screening tests can be done in the second trimester, including the '"quadruple blood test'" which screens for Down syndrome, Edwards syndrome (trisomy 18) and neural tube defects (NTDs). Another ultrasound can be done between 18 and 22 weeks to look for physical defects to the brain, spine, facial features, abdomen, heart and limbs.

Screening tests are all non-invasive and very accurate for the existence of risk—although there is always a small chance of a false-positive. Screening can not tell you if your baby will have any kind of disorder—only if they are at high or low risk for certain disorders. When assessed together, these blood tests and ultrasounds can provide a comprehensive assessment of many risk factors that could impact your baby's health and development.

'"Together the scan and blood test are around 95 percent to 98 percent accurate, but they never specifically confirm a diagnosis because they are only a screen,'" said Kathy Fray, senior midwife and maternity consultant.

The results of screening can be confusing, but a genetic counselor can help you assess the results and decide on next steps. Should your screening tests reveal a high level of risk for certain disorders, you may consider opting for genetic diagnostic testing.

Diagnostic tests

Diagnostic tests are a chance to look closer and determine if a genetic disorder or aneuploidy (a condition of having missing or extra chromosomes) is likely present. These tests are done on the cells of the fetus or placenta, and are considered invasive.

An amniocentesis is a procedure that uses a very thin needle to sample and test the amniotic fluid. '"There are risks,'" warned Kecia Gaither, M.D., OB-GYN, director of Perinatal Services at NYC Health + Hospitals/Lincoln. These include '"bleeding, infection [and] possible pregnancy loss.'"

'"But the risks are minuscule—less than one percent, generally,'" Gaither continued. '"The amniotic fluid that is removed is made up when the fetus urinates again.'"

A chorionic villus sampling (or CVS) is when a sample of tissue is taken from the placenta. CVS presents a slightly higher risk of miscarriage than the amniocentesis—but the risks are extremely low for both.

'"Nothing is 100 percent,'" Gaither said. But these two tests '"offer the highest certainty for diagnosis.'"

The role of a genetic counselor
Illustration by Joshua Christensen

There are so many people who can help you along your journey to becoming a parent. You're probably already familiar with your OB-GYN and perhaps you plan on working with a midwife and/or doula. A genetic counselor might be another member of your pregnancy team.

Katie Sagaser, a genetic counselor with Johns Hopkins Medicine, typically sees patients who were referred by their OB-GYN or high risk OB specialist. Most people don't consider turning to genetic counselors until after they become pregnant, but Sagaser says she's hopeful more and more people are considering the relevance of genetic counseling prior to pregnancy.

'"It would be really useful for people who are considering their reproductive options to talk to their gynecologist about a preconception consultation with a genetic counselor,'" Sagaser advised.

Whether it's preconception or sometime during pregnancy, genetic counselors can review family history, the health of the parents and any concerns about genetic or chromosomal abnormalities, then offer options for screening and diagnostic testing. They can help you navigate the complicated web of risk factors and testing options—and how much information you want to know.

If your doctor has referred you to a genetic counselor, it's helpful to gather as much information about your family's medical history as possible, to share with your counselor at the time of your first appointment.

But don't stress if that information isn't available. Gaither says there are a number of reasons that can limit someone's access to their family's medical history, and no one should feel bad or self-conscious if they don't have that information.

'"I like to remind folks that ultimately, we can only know what people have told us anyway,'" she said. '"So there's a lot about family health history that's always going to be a little bit enigmatic.'"

Weighing your options
Illustration by Joshua Christensen

Prenatal genetic testing may present you with difficult decisions—and preparing for those decisions in advance can ease some nerves about the process.

The first choices you'll be faced with are whether to do screening or diagnostic testing, and what you want to test for. A genetic counselor can advise you on these options, based on known risk factors and your level of desire for more information.

Most genetic screening and testing will come back negative, which means no anomalies were detected. With this peace of mind, you can get on with planning how to decorate the nursery and which stroller to buy. But pregnant people and couples should consider the possibility of positive results, and what they would do with that information.

'"I hope you come into this curious,'" Sagaser said. '"This [is] knowledge that can be empowering.'"

But there are certain rare conditions that may indicate a poor prognosis for the fetus' chance of surviving pregnancy and delivery, or the potential for a short lifespan—which is heartbreaking news for any couple. Other conditions are manageable or treatable.

'"Will they terminate the pregnancy if a genetic anomaly is found?'" Gaither said couples should ask themselves this question. '"If the answer is yes, they should consider having the test.'"

But whether or not a fatal or debilitating abnormality would lead someone to terminate a pregnancy is far from the only reason for testing.

'"Even if ending a pregnancy is off the table, there are obstetrical considerations,'" Sagaser said, adding that even couples who would never consider aborting a pregnancy should consider the benefits of the knowledge they could obtain through prenatal genetic testing.

Parents might prepare differently for the arrival of a baby with certain disabilities, or they may wish to alter their birth plan in preparation for a higher risk delivery. For example, Sagaser said if the testing shows a high risk for Down syndrome, and that couple lives in a rural geographic area—it would be safer to plan on delivering at a hospital with a higher level neonatal intensive care unit. Without that information, they will not be able to make that decision.

'"I try to get my patients to think broadly about this,'" said Sagaser, in how they would handle the results of genetic tests.

But there is also the argument that prenatal genetic testing introduces stress and anxiety to a pregnancy—and that should be avoided.

'"It is very important to note that the journey can become a hugely stressful emotional rollercoaster that is difficult to step off,'" Fray said.

Some couples choose not to test because the results would not impact any of their decisions or behavior surrounding the pregnancy. They may feel the information they might obtain is not worth the emotional turmoil of testing. That is a decision that is deeply personal, and while a genetic counselor can help in providing all of the information for an informed decision, it is ultimately up to the person or couple.

Genetic testing is a powerful tool that is becoming more and more prevalent in prenatal care and family planning. But just as every person parents differently, every person plans for parenting differently. There is no right or wrong choice when it comes to prenatal genetic testing—only options.