When you go to your first few checkups after finding out you’re pregnant, your provider will likely ask if you’d like to do any prenatal genetic screening. But what does this even mean? And how is it done? We’ll fill you in.
What Is Prenatal Genetic Screening?
Prenatal genetic screening helps expecting parents understand whether their baby has more or less of a chance to have certain birth defects, many of which are genetic disorders.
Genetic disorders are caused by imbalances in chromosomes. For example, in a trisomy there is an extra chromosome; however, in a monosomy a chromosome may be missing. Inherited disorders can be caused by mutations in genes and can include things like cystic fibrosis and sickle cell disease.
It's important to note that while prenatal screening tests can indicate an increased risk of your baby having a genetic disorder, they can't make a diagnosis. If your health-care provider has concerns about your genetic screening results, they will discuss your options for diagnostic testing.
Types of Prenatal Screening
There are three different types of prenatal screening tests:
First Trimester Screening
Between 10-13 weeks your provider may offer a blood test and ultrasound exam to screen for genetic disorders. The blood test will measure the level of certain substances. The ultrasound measures the thickness of the space at the back of baby’s neck (known as nuchal translucency screening). Abnormal measurements in both can mean that the fetus is at an increased risk of Down syndrome (trisomy 21) or another condition. Abnormal results from first trimester screening can also indicate physical defects of the heart, abdominal wall, or skeleton.
Second Trimester Screening
The second trimester screening includes another blood test known as the "quad screen." This blood test that measures the levels of four different substances in the blood, and can show the risk of certain chromosomal conditions like Down syndrome, Edwards syndrome (trisomy 18) and neural tube defects. Your provider can pair these results with the results of your anatomy ultrasound (done between 18-22 weeks’ gestation), which checks for defects in the brain, spine, facial features, abdomen, heart and limbs.
The results of the first and second trimester screenings may be combined in various ways to come to a more accurate test result.
Cell-Free DNA Testing
When you’re pregnant, a small amount of fetal DNA releases from the placenta into a pregnant person’s blood stream, known as cell-free DNA. Cell-free DNA can be screened for specific chromosome issues, and can also show baby’s sex and Rh blood type. This test can be conducted around 10 weeks of pregnancy, and typically takes up to 1 week to get the results.
What Do the Results of Prenatal Screening Tests Mean?
All prenatal screening results are reported as the amount of risk that a disorder might be present in your baby. For instance—a positive screening result for a genetic disorder means that your little one is at a higher risk as compared to the general population, but does not mean they definitely have it.
Similarly, negative results mean the fetus is at a lower risk of having a certain condition, but doesn’t entirely rule out the possibility. As with most testing, there is a possibility of false-positive or false-negative results, where the result simply isn’t accurate. It’s important to discuss testing and accuracy rates with your provider.
Should I Get Prenatal Genetic Screening?
This is truly your choice, and something you should work with your partner and provider to determine. You can use your personal belief and value systems as a guide — how would you use the results in your pregnancy care? Some parents want to know if their baby is at risk for a disorder so they can have more time to plan and prepare for medical care. Some parents may decide to end their pregnancy depending on their situation and results. Other parents decide not to do genetic screening or follow-up diagnostic testing at all.
There simply isn’t any one way to do it. Pregnancy, motherhood, and the choices you make are all extremely personal, and this choice is no different, mama.