Pregnancy already comes with a lot of questions and emotions. You might be waiting to do a prenatal genetic test to decide what pregnancy option you want to move forward with.
We also understand that prenatal genetic testing can sometimes add even more uncertainty, especially when results are unclear or unexpected. These blood tests are screening tools, not definitive diagnoses. Let’s look at what prenatal genetic testing is, what the results mean, its accuracy, if it’s the right next step for you.
Please note: this article is for informational purposes only and is not a substitute for medical advice, diagnosis, or treatment. Always consult a healthcare professional for medical concerns or emergencies.
Prenatal Genetic Testing Explained: Accuracy, False Positives, and Next Steps
What Is Prenatal Genetic Testing?
Prenatal genetic testing is an optional blood test typically done after 10 weeks of pregnancy that screens for certain chromosomal conditions or genetic disorders a fetus may have.
There are two types of prental testing: screening tests and diagnostic tests.
Screening tests estimate the likelihood of a condition being present, but they cannot diagnose a disorder. Diagnostic tests are used to confirm whether a condition actually exists.
Because screening tests are not definitive, false positives and false negatives can happen. An abnormal result does not automatically mean the fetus has a condition, and a normal result cannot completely rule one out.
Depending on the results, healthcare providers may recommend follow-up diagnostic testing for confirmation. Invasive diagnostic tests (such as CVS and amniocentesis) can increase the risk of miscarriage, so it is important to discuss risks and benefits with your healthcare provider.
For some women, prenatal testing provides reassurance and helps them prepare for the future. For others, it may create additional stress or anxiety during pregnancy. This is one reason some women choose to wait for second-trimester routine screening and ultrasound.
What does Noninvasive Prenatal Testing (NIPT) test for?
Most Noninvasive Prenatal Testing (NIPT) screens for:
- Trisomy 21 (Down Syndrome)
- Trisomy 18 (Edwards Syndrome)
- Trisomy 13 (Patau Syndrome)
Many tests can also identify fetal sex by detecting Y chromosomes in the mother’s blood sample.
NIPT cannot diagnose conditions, so it cannot tell you for certain if a fetus has a genetic disorder.
Not all testing screens for the same conditions. It’s important to talk to your healthcare provider about what screenings they offer, their accuracy, and whether NIPT is a good option for you. You can ask questions like:
- Is this testing recommended for my pregnancy?
- What conditions does this test screen for?
- How accurate is it?
- What happens if results come back abnormal?
If you got an abnormal result back and are considering ending your pregnancy, it is a good idea to be educated on abortion risks, side effects, and have a pre-abortion screening done in advance to ensure your safety and certainty about this decision.
How accurate are blood tests for gender?
An NIPT test’s primary purpose is to screen for genetic disorders. But it can confirm gender by picking up Y chromosomes which indicates a male. If there are no Y chromosomes, a female sex is predicted.
Accuracy of NIPT for predicting fetal sex is 99% accurate when done after 10 weeks of pregnancy.
Without a blood test, gender will be confirmed at a routine anatomy ultrasound appointment at 18 to 22 weeks.
What a “positive” NIPT test result actually means.
A positive NIPT does not mean the fetus has been confirmed with a specific chromosomal condition. What it does mean is that there could be a higher risk of having one. Even a negative result doesn’t rule out the possibility of a condition, it just means it’s a lower chance. NIPT is a screening test, not a diagnostic test. It is merely telling you there is a possibility, and further dialogist testing is recommended to confirm.
If you get testing done too early (before 10 weeks), the results could be less reliable due to only small amounts of the baby’s DNA in your blood.
A positive screening results should always be followed up with diagnostic testing to confirm the results and actually diagnose a disease.
Empower SAV would be happy to help you process and talk through next steps.
What causes a false positive NIPT test?
A few things can cause a NIPT false positive:
- Testing done before 10 weeks
- Placental mosaicism
- Vanishing twin syndrome
- Maternal genetic abnormalities
This is why it is so important to consider all possibilities of a false positive before making any major decisions about the pregnancy.
How common is a NIPT false positive?
NIPT is generally accurate in detecting Down Syndrome. False positives for Down Syndrome are about 0.1% to 0.2% of cases.
However, it is not as accurate at screening for other chromosomal abnormalities. NIPT is more likely to produce false positive or negatives for Trisomy 18 and 13.
Follow up diagnostic testing is crucial before making a pregnancy decisions based on a screening test.
How long does a NIPT test take?
It depends on the type of test you had. Results typically take 3-8 business days from the day your lab work is received.
Questions to Ask Yourself Before Deciding to Get Prenatal Genetic Testing:
1. Why do you want genetic testing during pregnancy?
Genetic testing and gender blood tests are completely optional. Figuring out what your personal beliefs and values are can help you make a decision that is best for you.
Are you a higher-risk pregnancy? Does your family have a history of genetic disorders? Are you a planner and want to be prepared? Do you just want the testing to determine the sex of the fetus? Will testing bring you peace of mind or worry?
Talk to your healthcare provider about your risk factors and if testing is necessary. If you are early in your pregnancy and aren’t sure what pregnancy option you want to move forward with, our licensed medical professionals at Empower SAV are here for you.
2. How will the results affect you emotionally?
Will knowing or will not knowing the results give you more anxiety? Will the possibility of inaccurate results have you up at night worrying?
It’s okay to choose to not do something you’re not comfortable with.
3. What will you do with the information?
If you are a planner, you might want to know if the fetus will have a genetic defect to start planning medically, emotionally, and financially. Others may face difficult decisions about how they want to move forward in their pregnancy.
Talking to a licensed medical professional can help you through this thought process. We are here for you.
You don’t have to navigate this decision alone.
Pregnancy can be overwhelming. There’s a lot of new information and decisions coming your way. Empower SAV in Savannah, GA’s compassionate team of licensed medical professionals and client advocates are here to offer medical advice and support through your pregnancy all at no cost.
You are not alone.