At some point during pregnancy, anywhere from 10 weeks to 22 weeks, all women are usually handed a brochure from their OBGYN’s office that lets them know their options for genetic screening in pregnancy.
This is typically known as “second trimester screening,” although new technology offers some testing as early as 10 weeks, which is still in the first trimester. These tests either screen for or diagnose birth defects in the fetus.
All of the options for this type of testing can feel overwhelming. Likely you’ve made a lot of emotional decisions up to this point regarding your pregnancy, and to be offered yet another option that could influence your decision regarding carrying to term can feel daunting.
Ultimately, this is a very personal decision for expecting parents and their OBGYN. There are many reasons to choose any of the options depending on your personal situation and other factors, such as insurance coverage. Many women opt to avoid all genetic screening.
In this article, I will try to break down all the types of testing available and the risks and benefits of doing genetic testing in pregnancy.
What do prenatal genetic tests check for?
Prenatal genetic tests fall into two categories: screening or diagnostic. They are also considered either invasive or non-invasive. Screening tests are non-invasive blood tests that check to see if you have a higher likelihood of having a fetus with genetic/prenatal abnormalities. These tests are aimed at screening many different conditions including:
Down syndrome
Also known as trisomy 21, this syndrome is characterized by developmental delays and in some people, an increased risk of health problems. Children born with Down syndrome have an average life expectancy of nearly 60 years old.
Abdominal wall defects
These defects occur when parts of the abdominal contents, such as the intestines, protrude through the fetus’ belly button.
Neural tube defects/spina bifida
These defects occur when a portion of the neural tube fails to develop or close properly. The prognosis for children born with neural tube defects varies widely depending on the severity of the defect. These defects can often be seen on ultrasound. Some women are candidates for surgery to help correct these defects while the baby is still in the womb.
Trisomy 13 and trisomy 18
Trisomy 13 and 18 are chromosomal disorders characterized by intellectual and physical disabilities of varying kind and severity. Often the children born with these two trisomies do not live past age one due to life-threatening disabilities.
Sex chromosome abnormalities
These occur due to variations in the number of X and Y chromosomes present. Prognosis and presentation of symptoms varies widely between different syndromes, with many of these children remaining symptom-free until puberty.
What are the types of genetic screening offered in pregnancy?
Cell-Free DNA
Cell-free DNA is a blood test done after 10 weeks of pregnancy that screens for chromosomal abnormalities in a fetus. It screens for Down syndrome, trisomy 18, trisomy 13, and sex chromosome abnormalities. You can also learn the gender of your child from this test.
Triple/Quad Screening
This is a blood test done between 15-22 weeks that checks levels of three or four blood markers that if elevated in certain patterns indicate an increased risk for conditions such as Down syndrome, neural tube defects, trisomy 18, and abdominal wall defects.
Both of these tests are considered non-invasive, meaning they are done through a blood test and carry no risk of miscarriage.
How accurate is prenatal genetic screening?
Cell-free DNA screening can detect more than 99% of Down syndrome, 97% of trisomy 18, and 87% of trisomy 13 pregnancies. It is not as accurate for twin pregnancies and is not used for triplets or greater. Other factors such as BMI greater than 30 (obesity) and taking blood thinners can also decrease the accuracy of cell-free DNA testing.
The quad screen correctly identifies about 80% of Down syndrome pregnancies. About 5% of women have a false positive result, meaning that the test result is positive but the baby doesn't actually have Down syndrome. Factors such as a pregnancy with multiples, diabetes, and incorrect dating of a pregnancy can decrease the accuracy of this test.
Does insurance cover genetic screening?
This completely depends on the type of insurance you have and what state you live in. Medicaid covers prenatal genetic screening in 36 states and DC. Most basic insurance plans do not cover cell-free DNA screening for women with no risk factors (under 35 years old who have no history of pregnancies with abnormalities), which is why many women interested in prenatal screening opt for the quad screen.
If you are interested in early genetic screening by blood test, it is a good idea to call your insurance company and ask what tests are covered.
Why do genetic screening?
Some expectant mothers want to know if their fetus has any birth defects, as it will affect her decision whether or not to carry to term. Others want to find out to be able to mentally prepare themselves for the reality of caring for a child with birth defects.
Some medical providers will encourage their patients to be screened due to their increased risk factors for genetic diseases. For example, advanced maternal age is an increased risk factor for Down syndrome.
Some may consider it medically beneficial to be prepared for the delivery of a child with birth defects; however, most birth defects requiring medical attention are once again screened for at the 20 week ultrasound and right after the baby is born.
Many people decide to do the cell-free DNA test to be able to find out the gender of their child as soon as possible.
Why do some people opt out?
Many women have made the decision to carry a pregnancy to term regardless of possible birth defects, and therefore feel there is no reason for another test (which may end up being expensive, depending on medical insurance).
Since the screening tests cannot definitively diagnose any birth defects, many choose to avoid testing due to the unnecessary anxiety a positive result could cause. If the pregnancy is high risk and the expectant mother has concerns for miscarriage, they may decide to avoid invasive diagnostic tests, such as an amniocentesis, which carries a risk for miscarriage (more on this later).
Many choose to wait for the ultrasound that happens around 20 weeks of pregnancy (sometimes called the anatomy scan), which provides a lot of the same information as these earlier tests and is generally covered by insurance. This ultrasound checks for major physical defects in the fetus’ brain, spine, facial features, abdomen, limbs, and heart, and is typically where you have a chance to learn the gender.
When my mother was pregnant with me, her quad screen came back abnormal. Her doctor’s office called on a Friday afternoon to let her know that her blood work showed an increased risk of her baby having Down syndrome. She told me she worried and grieved for this change in her plans for the entire weekend, only to be told by her doctor the following Monday that the test does often have false positives.
Having been told this by my mother, I decided against doing any screening during my pregnancy since I had decided to continue my pregnancy regardless. I felt satisfied that testing later in pregnancy would be sufficient to help prepare for any medical care needed should my child have a birth defect.
What happens if your second trimester screening is abnormal?
If you have an abnormal test, you will likely be offered additional diagnostic tests by your medical provider, depending on what came back abnormal. Often, an ultrasound is performed and your provider may offer one of two diagnostic procedures called amniocentesis or chorionic villus sampling. These are invasive procedures where a needle is used to collect cells from the amniotic fluid or placenta (respectively).
Amniocentesis is usually done between 15-20 weeks and carries a slight risk of miscarriage. It can test for both Down syndrome and neural tube defects.
Chorionic villus sampling, which is not useful in diagnosing neural tube defects, is done earlier, between 10-13 weeks, but carries a higher risk of miscarriage than amniocentesis.
As with the screening tests, these tests are completely optional and may not be covered by insurance. Many health care systems offer referrals to genetic counselors so that you can discuss your options and risks in greater detail and have all of your questions answered.
Take a Deep Breath
If you are feeling overwhelmed at this point, take a deep breath..
Talk to your OBGYN about your options, risks, and his or her own recommendations. And try not to stress about these tests. Remember, birth defects are relatively rare and many children with prenatal abnormalities go on to have amazing lives!