Learn more about your baby with second-trimester prenatal screenings
Pregnancy is such an exciting time! Whether this is your first baby or you've done this many times before, there's still lots to learn as you go through your trimesters.
During your first trimester, you may undergo initial prenatal screening tests, which can help you learn more about your baby and help your healthcare provider understand if he or she is at high risk for certain genetic conditions.
The first-trimester screening includes an ultrasound of your baby and bloodwork from you. You’re able to start seeing your baby, discover his or her gender (if you choose!) and undergo prenatal screening tests to learn even more about your little one.
As you move into your second trimester, you'll be able to undergo further testing. You’ll be reaching some exciting milestones with your little one during this time! From hearing their heartbeat(s) to learning their gender(s), your second trimester is truly amazing.
“During this time, your health provider will talk with you about a number of prenatal screening tests that are available,” says Lindsay Bailey, a genetic counselor at Geisinger. “Often between weeks 15 and 22, you’ll be offered a test for birth defects, as well as chromosomal conditions. It’s important to understand that all prenatal screening tests are optional. Ask your health provider if you’re unsure which ones are best for you.”
These tests do not diagnose your baby with a condition but will indicate if further testing should be performed. Here are some common second-trimester prenatal screening tests.
The quad screen test
Between 15 and 22 weeks of pregnancy, you’ll have the option to receive a blood test called a quad screen.
The quad screen measures four hormones or proteins in the maternal bloodstream and, based on the levels of those hormones or proteins, you’ll be given a risk for your baby having certain conditions:
- Chromosomal conditions, such as:
- Trisomy 21 (Down syndrome)
- Trisomy 18 (Edwards syndrome)
- Neural tube defects, also known as spina bifida
“A positive screening test does not mean your baby has one of these conditions,” explains Ms. Bailey. “However, it does mean that your baby is at a higher risk of being born with these. Your health provider will discuss further testing to learn more.”
Quad screen test results are reported as a risk number: For example, one in five or one in 5,000, versus a “yes or no” answer.
If you choose to receive the quad screen test, your blood will be drawn and sent to a lab for testing. The results will take about one week.
Cell-free fetal DNA (non-invasive prenatal testing)
This relatively new screening test can help assess the risk of your baby being born with certain chromosomal disorders. Offered as early as your tenth week of pregnancy and if you’re considered a high-risk pregnancy, the cell-free fetal DNA screening is not used to diagnose your baby, rather it will help you and your health provider decide if further testing should be done.
“Cell-free fetal DNA is released by the placenta and enters the mother's bloodstream during pregnancy,” explains Ms. Bailey. DNA information from the pregnancy is screened from chromosome conditions, such as trisomy 21, trisomy 18, trisomy 13 and sex chromosome conditions.
“While this test does screen for some of the same chromosomal conditions as the quad screen test, it does not screen for neural tube defects. So it may be recommended to also have a second blood test to screen for neural tube defects,” notes Ms. Bailey.
If your pregnancy is considered high risk, this may be the best test for you.
Examples of high-risk pregnancies include those where:
- The mother is age 35 or older
- The mother had a previous pregnancy with a chromosome condition
- The mother is currently pregnant and has had a birth defect or positive screening tests, such as the quad screen or first-trimester screen
This test involves drawing blood and is completely safe for both mom and baby.
Amniocentesis
After an abnormal or positive screening test, your health provider may discuss an amniocentesis test with you, based on your results. During an amniocentesis, a thin needle will be inserted into your abdomen and into the amniotic sac to remove fluid for testing.
“The fluid in the amniotic sac contains cells shed by your baby and can be further tested to determine whether he or she may have a chromosomal condition. It can provide a definite diagnosis with a ‘yes or no’ answer,” explains Ms. Bailey. “Before choosing to undergo prenatal screening tests, discuss the risks as well as the benefits with your health provider to learn as much as possible before making a decision.”
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