Genetic testing during pregnancy offers insights into a baby’s genetic health. These tests help parents understand potential risks or conditions. They inform decisions throughout pregnancy. Many of these tests provide risk assessments rather than definitive diagnoses.
Types of Genetic Tests in Pregnancy
Genetic tests during pregnancy are categorized as screening tests and diagnostic tests. Screening tests assess the likelihood of a baby having certain genetic conditions. They are non-invasive and pose no direct risk. Diagnostic tests provide a definitive answer about a specific genetic condition. They are more invasive and carry a small risk.
Non-Invasive Prenatal Testing (NIPT) is a common screening test, performed as early as 10 weeks. It analyzes fetal DNA in the pregnant person’s blood to assess the risk of chromosomal abnormalities. Carrier screening, often done before or during pregnancy, determines if parents carry genes for inherited conditions like cystic fibrosis or spinal muscular atrophy. First and second-trimester screens, using blood tests and ultrasounds, also assess risk for conditions like Down syndrome and Trisomy 18.
Diagnostic tests are considered if a screening test indicates increased risk or other factors suggest a higher chance. Chorionic Villus Sampling (CVS) can be performed earlier, between 10 and 13 weeks by sampling the placenta. Amniocentesis involves collecting amniotic fluid between 15 and 20 weeks. Both analyze the baby’s genetic material directly, offering conclusive results.
Key Terminology and Concepts
Understanding key terms helps when reviewing genetic test results. “Screening” refers to tests that identify a higher or lower chance of a condition, while “diagnostic” tests provide a definitive answer. Results often use “high risk” or “low risk,” reflecting statistical probabilities, not certainty. A “positive” screening result means an increased chance, not a diagnosis, while a “negative” result suggests a lower chance.
Aneuploidy describes an abnormal number of chromosomes in a cell, differing from the usual 46. This involves an extra chromosome (trisomy) or a missing one. Common aneuploidies screened for include Trisomy 21 (Down syndrome), Trisomy 18 (Edwards syndrome), and Trisomy 13 (Patau syndrome). They arise from errors in cell division, leading to an imbalance in genetic material.
A “microdeletion” occurs when a tiny piece of a chromosome is missing. Their impact varies depending on the genes involved. “Carrier status” indicates an individual carries one copy of a gene variant that, if inherited from both parents, could cause a genetic condition in their child, though carriers typically show no symptoms. A “variant of uncertain significance” (VUS) is a genetic change where its connection to a health condition is unclear due to insufficient information. VUS findings are not actionable for clinical management until more data is available.
Interpreting Specific Test Results
Interpreting genetic test results requires attention to the test type and context. For Non-Invasive Prenatal Testing (NIPT), results indicate “low risk” or “high risk” for conditions like Trisomy 21, 18, or 13. A “low risk” result means the chance is very small. A “high risk” result does not confirm a diagnosis but suggests increased probability, prompting further discussion and often diagnostic testing.
NIPT reports may present a “risk value,” such as “1 in 10,000,” indicating statistical likelihood. For example, a “1 in 10,000” risk means that for every 10,000 pregnancies with this result, one might have the condition.
The “Positive Predictive Value” (PPV) is important for high-risk NIPT results, representing the probability that a positive test is a true positive. PPV varies based on condition prevalence and pregnant person’s age. For instance, Trisomy 21 PPV can be high (e.g., 86.1%), but for rarer conditions or sex chromosome aneuploidies, it might be lower (e.g., 20% for Monosomy X), indicating a higher chance of a false positive.
Sometimes, NIPT yields a “no result” due to insufficient fetal DNA or other technical reasons. A re-draw or alternative testing may be recommended.
For carrier screening, results identify if an individual is a “carrier” for specific genetic conditions. If both parents are carriers for the same autosomal recessive condition, there is a 25% chance with each pregnancy their child will inherit two affected gene copies and develop the condition. There is also a 50% chance the child will be a carrier and a 25% chance they will not inherit the variant. Understanding these probabilities allows parents to consider family planning.
Diagnostic test results, such as those from amniocentesis or CVS, are definitive. These tests directly analyze the baby’s chromosomes or genes, providing a clear indication of whether a specific abnormality or condition is present or absent. A positive diagnostic result confirms the condition’s presence, while a negative result confirms its absence for the conditions tested. These results are crucial for informed decisions about pregnancy management and preparing for the baby’s arrival.
Next Steps and Support
Receiving genetic test results often brings emotions, and understanding next steps is important. Always discuss results with a healthcare provider, such as an OB/GYN or genetic counselor. These professionals explain findings, clarify uncertainties, and relate results to individual circumstances. They provide personalized context, especially important for screening tests that provide risk assessments rather than diagnoses.
Genetic counselors are trained to interpret complex genetic information and guide individuals through results. They offer support, helping families understand options, including follow-up tests if a screening test indicates increased risk. For example, a high-risk NIPT result typically leads to a recommendation for a diagnostic test like amniocentesis or CVS to confirm the finding. Genetic counselors also provide emotional support and help explore decisions regarding pregnancy management and future planning, regardless of the test outcome. They connect families with resources and support networks, ensuring individuals feel informed and supported.