Unlike general pregnancy screening — which may include infection testing, blood sugar screening, or ultrasound evaluation — prenatal genetic screening is designed to provide information about the likelihood a pregnancy may have certain genetic conditions.
How Does Prenatal Genetic Screening Work?
Most prenatal genetic screening tests are performed using a blood sample from a pregnant individual and are typically offered early in pregnancy, even as early as 9 weeks.
Carrier screening can be performed before or during a pregnancy. It looks at the parent’s DNA to determine if they carry any genetic changes associated with a condition that can be passed on to their baby. Typically, these genetic changes have to be inherited from both parents in order for a baby to be affected or have symptoms.
During pregnancy, tiny pieces of DNA from the pregnancy can be found in maternal blood. This is known as cell-free DNA (cfDNA). Prenatal tests can use cfDNA to estimate the likelihood of your baby having certain inherited or chromosomal conditions. It is important to remember that these tests are not diagnostic. They are meant to give you and your healthcare provider more information to determine the best next steps for your pregnancy.
What Conditions Does Prenatal Genetic Screening Evaluate?
Prenatal genetic screening generally evaluates two main categories of conditions: chromosomal conditions and inherited genetic conditions.
Chromosomal Conditions
Chromosomal conditions are caused by an extra or missing chromosome and usually happen by chance. Every pregnancy carries a small risk for these conditions, regardless of family history.
Common examples include:
- Down syndrome (Trisomy 21)
- Edwards syndrome (Trisomy 18)
- Patau syndrome (Trisomy 13)
- Certain sex chromosome conditions
Inherited Genetic Conditions
Inherited genetic conditions are caused by changes in specific genes and are passed down from parents to their children.
This is why carrier screening is important: it identifies whether a parent carries a genetic change associated with certain inherited conditions. If a pregnant person is found to be a carrier of a certain condition, additional testing can be done that looks at cell-free DNA to determine the likelihood that their current pregnancy may be affected with that condition.
Some of these conditions include:
- Cystic fibrosis
- Spinal muscular atrophy
- Hemoglobin disorders
It is important to remember that prenatal genetic screening for both chromosomal and inherited genetic conditions is not diagnostic. They are meant to provide you and your healthcare provider with more information.
Understanding Genetic Screening Results
Results from prenatal genetic screening are typically categorized as low-risk or high-risk.
Low-Risk Result
A low-risk result means the screening test found a lower likelihood that a pregnancy is affected with a condition being evaluated. Most low-risk results are reassuring. However, no screening test can detect all cases, and a low-risk result does not completely rule out the possibility of having an affected baby.
High-Risk Result
A high-risk result means the screening test found an increased likelihood that a pregnancy may have the condition being screened. A high-risk result does not mean a baby will be affected with this condition. Diagnostic testing, such as chorionic villus sampling (CVS) or amniocentesis, is typically recommended to determine whether the condition is actually present.
Your healthcare provider can review your individual results and what they may mean for your pregnancy. It’s important to remember that screening tests cannot look for all genetic conditions and that false positives and negatives can occur.
Limitations of Prenatal Genetic Screening
Prenatal genetic screening has important limitations:
- It does not diagnose a condition.
- Not all genetic conditions are evaluated.
- False positive and false negative results can occur.
- Results may depend on biological factors such as placental DNA patterns.
- Additional testing may be needed to determine a result.
Understanding these limitations helps ensure screening results are interpreted appropriately.
When Genetic Counseling May Be Helpful
Genetic counseling may be recommended after a high-risk screening result, an inconclusive result, or when there are questions about testing options. A genetic counselor can review the details of a result, explain the difference between screening and diagnostic testing, and discuss potential outcomes and next steps.
The goal of genetic counseling is to provide clear, accurate information and support individuals in making decisions that align with their values and preferences.
Unity offers access to a team of board-certified genetic counselors who can help individuals understand their options, understand their screening results, and discuss next steps. Appointments can be scheduled through the patient portal, on the Unity website, or by contacting Client Services directly.
