What to Expect During Genetic Testing

In early pregnancy, your OB/GYN or healthcare provider will likely offer you the option of doing some genetic tests and screenings. Genetic tests can offer helpful information about your baby’s health, including the possibility of birth defects or genetic abnormalities.

These tests are usually recommended for people who have a family history of genetic disorders, or people who are having a baby over the age of 35. But anyone who’s interested and thinks they’ll find the information helpful can undergo genetic testing. Still, genetic testing isn’t for everyone, and it’s not required, especially if you don’t have a known risk factor.

Here's what to know about genetic testing, including what each of the most common tests are looking for, what testing involves, and how to know if genetic testing is right for you.

What Is a Genetic Test?

A genetic test is a test performed either prenatally or during pregnancy that assesses the chances that you may give birth to a baby with a genetic abnormality. There are two basic kinds of genetic tests, explains Austin Janaitis, MS, CGC, board certified genetic counselor at Mercy Medical Center in Baltimore, MD: screening tests and diagnostic tests.

“These tests each assess for different conditions but collectively they are screening for chromosome abnormalities, genetic disorders, and birth defects,” Janaitis explains. “Screening tests inform patients and providers of the risks for certain conditions but are unable to provide a diagnosis.” If a screening test indicates that your baby may have a genetic abnormality, a diagnostic test is usually performed to confirm whether this is the case.

Genetic tests may involve blood draws, ultrasounds, or procedures where genetic material is removed from a fetus (via amniotic fluid) or from the placenta. There are many chromosomal and gene abnormalities that these tests are looking for, but some of the most common ones include Down syndrome, trisomy 18, trisomy 13, sickle cell disease, cystic fibrosis, and Tay-Sachs disease.

What Are the Types of Genetic Tests?

When you begin the journey of genetic testing, you may be overwhelmed by all the different tests out there. You may be unsure of when the tests are done, what they involve, and what they are looking for. Let’s break down the different tests—chronologically, and by type.

Before Pregnancy

Carrier Screening

There’s basically only one type of test that is universally offered before you get pregnant, says Janaitis: a carrier screening test. “Carrier screenings help determine the risk for a future pregnancy to have a genetic disorder,” she explains. “This testing is performed by sequencing specific genes known to cause health disorders.”

Most of the time, carrier screenings look for recessive genetic disorders, which means that both parents have to be carriers for the baby to inherit the condition. Some of the conditions that carrier screenings typically test for include cystic fibrosis, Tay–Sachs disease, fragile X syndrome, and sickle cell disease.

First Trimester Screening Tests

Blood Screening Tests

The blood screening test perormed in the first trimester involves testing two different proteins: pregnancy associated plasma protein A (PAPP-A) and human chorionic gonadotropin (hCG). If these proteins are out of range—too low or too high—it might indicate a fetal genetic abnormality.

Ultrasound

During the first trimester, a type of ultrasound that measures the fluid in your baby’s neck may be performed. This is called a nuchal translucency screening. If the screening indicates that your baby has increased fluid behind the neck, they may be at increased risk of Down syndrome or heart defects.

Cell-Free DNA Screening

Also called NIPT, cell-free DNA screening is another test that may be performed in the first trimester. This is a non-invasive test that can identify fragments of fetal DNA in a pregnant person’s blood, explains Iris Insogna, MD, OB/GYN and reproductive endocrinologist at Columbia University Fertility Center.

“Generally, the test is specifically looking for chromosome number for chromosomes 13, 18, 21, X and Y,” Dr. Insogna describles. “Trisomies (an extra chromosome) of 13, 18 and 21 can lead to well-defined syndromes.”

For example, trisomy 21 is what causes Down syndrome, Dr. Insogna says. Additionally, she explains. the presence of X and Y chromosomes can tell you if you are carrying a female (XX) or male (XY) fetus, and whether your fetus may have sex chromosomes aneuploidies (an abnormal number of sex chromosomes).

First Trimester Diagnostic Tests

Chorionic Villus Sampling (CVS)

If any of your screenings indicate that an abnormality may be present, you will likely need a diagnostic test to confirm or deny the possibility. The diagnostic test typically done in the first trimester (between 10.5 weeks to 13.5 weeks) is called chorionic villus sampling (CVS). This test involves extracting and testing a small amount of placenta tissue.

Second Trimester Screening Tests

Blood Screening Tests

The genetic blood test you usually receive in your second trimester is something usually referred to as “quad” or “tetra screen,” says Janaitis. “This screening analyzes markers from maternal blood to determine the risk for Down syndrome, trisomy 18, and open neural tube defects (spina bifida),” she explains. This blood test is usually done between 15 and 20 weeks of pregnancy.

Ultrasound

Your 18-20 week ultrasound is usually the most extensive ultrasound you’ll get during pregnancy. This ultrasound checks your baby’s growth to make sure it’s on track, and also checks for birth defects in areas like the brain, spine, heart, stomach, limbs, and face.

Second Trimester Diagnostic Tests

Amniocentesis

If any of the screening tests performed in the second trimester indicate a problem, you will undergo a diagnostic test called an amniocentesis. “This diagnostic test utilizes an amniotic fluid sample to determine if a pregnancy is affected with a chromosome abnormality, specific genetic disorder, congenital infection, or other diagnosis,” explains Janaitis. Amniocentesis can be performed anytime after 15 weeks of pregnancy.

What to Expect During a Genetic Test

It’s common to have concerns about what happens during genetic testing. Many expectant parents are worried about the more invasive tests, and whether they may harm their fetuses. The experience you will have getting a genetic test varies quite a bit, and really depends on the test itself, says Dr. Insogna.

“Some genetic tests are simple blood tests,” she explains. These involve standard blood draws, and are not considered invasive. “The more invasive tests like CVS or amniocentesis involve carefully passing a needle through the abdominal wall and the uterine wall to take a sample of the placenta (for CVS) or amniotic fluid (for amniocentesis).”

It’s important to understand that the more invasive diagnostic tests, like CVS and amniocentesis, are done carefully and with safety in mind. Ultrasound technology is used during these procedures to ensure your provider doesn’t harm your fetus.

However, these tests are not completely risk-free, says Janaitis. “These tests require an instrument to  be inserted into the uterus to obtain these samples; therefore, there is a small risk for pregnancy complications related to these tests,” she says. “Complications from these procedures could result in infection, miscarriage, or preterm delivery, depending on the gestational age when performed.”

Still, she notes that the risk of pregnancy complications from these procedures are very low. For example, the risk of miscarriage from CVS is 1% ; for amniocentesis, the risk is less than 1%.

Is Genetic Testing Right For Me?

Genetic testing can be very helpful for some people. Such procedures may be strongly advised for people who have a family history of genetic abnormalities, or people who are over 35 and at higher risk of having children with birth defects. But genetic testing can be very stressful, and some of the screening tests can generate false positives, along with a need for more invasive testing.

The American College of Obstetricians and Gynecologists (ACOG) advises that you ask yourself a few guiding questions as you explore genetic testing. First, you should consult with your healthcare provider about your own medical risk factors. Then, you should ask yourself how much information you want to know about your baby. If you are prone to anxiety, results from genetic tests may not be helpful to you.

Finally, you should consider what you’d do if you found out that your baby had a genetic abnormality. Some parents might feel more comfortable than others proceeding with their pregnancies, some may feel more comfortable terminating the pregnancy, and some may not have access to abortion services.

A Word From Verywell

Every expectant parent is different, and there is no one “right” choice when it comes to whether or not you should undergo genetic testing. If you are unsure of what to do, please reach out to your healthcare provide or a genetic counselor who can assist you in understanding the risks and benefits of each test, and help you come to a decision that works for you and your family.