Prenatal testing — screening during pregnancy that can reveal whether a baby has certain conditions or chromosomal differences. For many expectant parents, this raises important questions: Which tests are available? Who should consider them? And what does a result actually mean?
Here is a clear overview of prenatal testing, with focus on the most common tests, what they can detect, and what to consider.
What Is Prenatal Testing?
Prenatal testing refers to examinations performed during pregnancy to look for congenital conditions, chromosomal differences, or structural abnormalities. There are two main categories:
- Screening tests: Give a probability assessment (e.g., first trimester screening, NIPT)
- Diagnostic tests: Give a definitive answer (e.g., amniocentesis, CVS)
Screening tests can indicate elevated risk but cannot confirm a diagnosis. Diagnostic tests can confirm or rule out a concern, but they carry a small risk of complications.
Prenatal testing is voluntary. No pregnant woman is required to have any of these tests. What matters most is making an informed choice based on what's right for you and your partner.
Who Should Consider Prenatal Testing?
Prenatal testing may be recommended or offered if you:
- Are 35 or older at the time of delivery
- Have previously had a child with a chromosomal condition
- Are a known carrier of a genetic condition (or have a partner who is)
- Have had abnormal findings on a routine ultrasound
- Have other medical reasons
In many countries, all pregnant women are routinely offered a first trimester ultrasound and blood screening. NIPT has become increasingly available, either through public health programs or as a private option.
Routine ultrasound mid-pregnancy (around 18–20 weeks) is offered to all pregnant women in many countries. While not technically diagnostic testing, it can reveal structural differences in the baby.
First Trimester Screening (Combined Screening)
First trimester combined screening is offered between weeks 11 and 14 of pregnancy.
What Is Measured?
- Nuchal translucency (NT) scan: Ultrasound measurement of the fluid at the back of the baby's neck. Increased fluid can suggest chromosomal differences.
- Blood tests: Two markers in the mother's blood are measured (PAPP-A and free beta-hCG)
- Maternal age: Incorporated into the risk calculation
What Can It Detect?
Combined screening gives a risk estimate for:
- Trisomy 21 (Down syndrome)
- Trisomy 18 (Edwards syndrome)
- Trisomy 13 (Patau syndrome)
Accuracy
Combined screening has a detection rate of approximately 85–90% for Down syndrome, with a false-positive rate of around 3–5%. This means some women receive a high-risk result even when the baby is unaffected.
NIPT — Non-Invasive Prenatal Testing
NIPT is a blood test from the mother that analyzes the baby's DNA (cell-free fetal DNA) circulating in the mother's bloodstream.
How Does NIPT Work?
During pregnancy, small fragments of DNA from the placenta circulate in the mother's blood. NIPT analyzes this DNA to look for chromosomal differences. The test can be performed from week 10 onward.
What Can NIPT Detect?
- Trisomy 21 (Down syndrome) — detection rate over 99%
- Trisomy 18 (Edwards syndrome) — detection rate over 97%
- Trisomy 13 (Patau syndrome) — detection rate over 99%
- Sex chromosome differences (Turner syndrome, Klinefelter syndrome, and others)
- Baby's sex (if desired)
Accuracy
NIPT is significantly more accurate than combined first trimester screening:
- Detection rate: over 99% for trisomy 21
- False-positive rate: under 0.1%
- However, NIPT is still a screening test — not a diagnostic test
NIPT is highly accurate, but it remains a screening test. An abnormal NIPT result should always be confirmed with a diagnostic test (amniocentesis or CVS) before any decisions are made.
NIPT Availability and Cost
- NIPT is available privately in most countries and is increasingly covered by insurance or public health programs for high-risk pregnancies
- Private testing typically costs between $200–$500 depending on location and provider
- Results typically come back within 7–14 days
Amniocentesis
Amniocentesis is a diagnostic test that provides a definitive answer about the baby's chromosomes.
How Is It Performed?
- Usually performed between weeks 15 and 20
- A thin needle is inserted through the abdomen and uterine wall under ultrasound guidance
- A small amount of amniotic fluid (about 15–20 ml) is withdrawn
- The fluid contains cells from the baby, which are analyzed
What Can It Detect?
- All chromosomal differences (trisomies, deletions, translocations)
- Certain gene variants (if specifically tested)
- Baby's sex
Risks
- Risk of miscarriage: approximately 0.1–0.5% (about 1 in 200–1,000)
- Some discomfort during the procedure
- Mild cramping afterward, which typically resolves quickly
The doctor considers the position of the placenta when choosing the safest point of entry.
CVS — Chorionic Villus Sampling
CVS is a diagnostic test that can be performed earlier in pregnancy than amniocentesis.
How Is It Performed?
- Usually performed between weeks 10 and 13
- A thin needle or small tube is used to take a tissue sample from the placenta
- Can be done through the abdomen or through the cervix
- Cells from the sample are analyzed for chromosomal differences
Advantages and Disadvantages
Advantages:
- Can be performed earlier than amniocentesis
- Results come back faster (usually within 1–2 weeks)
Disadvantages:
- Risk of miscarriage: approximately 0.5–1% (slightly higher than amniocentesis)
- In rare cases, results can be uncertain due to placental mosaicism
Routine Ultrasound During Pregnancy
While the mid-pregnancy anatomy scan (around 18–20 weeks) is not technically prenatal testing, it's worth noting what it can show:
- Baby's size and growth
- Placental position and condition
- Amniotic fluid levels
- Number of babies
- Structural differences (heart, brain, spine, organs)
- Baby's position
The Process: Step by Step
1. Information and Counseling
Before any prenatal testing is offered, you should receive thorough information from your doctor or midwife about:
- Which tests are relevant for your situation
- What the tests can and cannot detect
- Risks of invasive procedures
- What an abnormal result might mean
- Your own and your partner's values and preferences
2. Screening Test (Combined Screening or NIPT)
If you choose screening, the test is performed. Results typically come back within 1–2 weeks.
3. If Risk Is Elevated
If a screening test indicates elevated risk, you will be offered genetic counseling and the option of a diagnostic test.
4. Diagnostic Test
If you choose a diagnostic test, it is performed under ultrasound guidance. Results come back within 1–3 weeks depending on the test.
5. The Result
- Normal result: You can breathe easier
- Abnormal result: You will be offered genetic counseling, detailed information, and time to process
Regardless of the result, you are entitled to support and guidance. Hospitals have genetic counselors and social workers who can help you through the process.
Ethical Considerations
Prenatal testing raises important ethical questions worth reflecting on:
- Why do you want the tests? What will you do with the information?
- How would you respond to an abnormal result?
- Can you live with uncertainty if you choose not to test?
- Consider talking with your partner, family, or a counselor
There are no right or wrong answers. What matters most is that you make an informed choice you can stand behind.
Frequently Asked Questions
Is NIPT harmful to my baby?
No, NIPT is completely safe. It is a standard blood draw from the mother. There is no risk to the baby.
Can NIPT replace amniocentesis?
NIPT cannot replace amniocentesis as a diagnostic test. NIPT provides a risk estimate through screening, while amniocentesis gives a definitive answer. An abnormal NIPT result should always be confirmed with a diagnostic test.
How early can NIPT be performed?
NIPT can be performed from week 10. The test requires sufficient fetal DNA in the mother's blood, which increases as the pregnancy progresses.
Is NIPT covered by insurance?
In many countries, NIPT is covered for pregnancies with elevated risk (maternal age over 35, known genetic risk, abnormal ultrasound findings). Availability and coverage vary by country and insurance plan. Check with your provider.
Can I choose not to know the baby's sex?
Yes, you can request that the sex not be reported with NIPT or other testing. Let your doctor or the laboratory know your preference.
How long does it take to get results?
- Combined first trimester screening: usually 1–2 weeks
- NIPT: usually 7–14 days
- Amniocentesis: rapid results within 2–3 days (for common trisomies); full results 2–3 weeks
- CVS: 1–2 weeks