How Is a DNA Test Done During Pregnancy?

Learn how non-invasive prenatal testing (NIPT) uses cell-free DNA to screen for chromosomal conditions. Understand NIPT procedure, accuracy, and next steps. US guide.

A DNA test during pregnancy is typically performed using a simple blood draw from the mother, which analyzes cell-free fetal DNA (cffDNA) circulating in her plasma. This method, called non-invasive prenatal testing (NIPT), is a highly accurate screening tool for common chromosomal conditions like Down syndrome, Edwards syndrome, and Patau syndrome. Unlike older invasive procedures, NIPT poses no risk to the pregnancy and is routinely offered to women in the United States starting at 10 weeks of gestation.

What Is Non-Invasive Prenatal Testing (NIPT)?

NIPT, also known as cell-free DNA screening, is a modern prenatal screening test that examines fragments of fetal DNA present in the mother’s bloodstream. During pregnancy, a small percentage of the DNA in the mother’s blood comes from the placenta, which genetically matches the fetus. This cell-free DNA (cfDNA) can be isolated and analyzed to assess the risk of certain chromosomal abnormalities. NIPT is considered a screening test, not a diagnostic test; it indicates whether the risk is increased or decreased, but a positive result typically requires confirmation with a diagnostic procedure like chorionic villus sampling (CVS) or amniocentesis.

How Does NIPT Work?

The process involves a standard blood draw from the mother’s arm, similar to routine lab work. The blood sample is sent to a specialized laboratory where the cell-free DNA is extracted, sequenced, and analyzed. The lab measures the relative amount of DNA from each chromosome. An excess or deficit of DNA from a specific chromosome can indicate a trisomy (e.g., three copies of chromosome 21 for Down syndrome) or a sex chromosome abnormality. The test also determines fetal sex and can sometimes detect microdeletions. Results are typically available within 5 to 10 business days.

What Conditions Does NIPT Screen For?

• Common trisomies: Trisomy 21 (Down syndrome), Trisomy 18 (Edwards syndrome), Trisomy 13 (Patau syndrome)
• Sex chromosome aneuploidies: Turner syndrome, Klinefelter syndrome, and others
• Selected microdeletions: Such as 22q11.2 deletion syndrome (DiGeorge syndrome), though not all panels include these
• Fetal sex (if desired, sometimes used for X-linked disorders)

Note: NIPT is not a comprehensive test for all genetic conditions. It does not screen for neural tube defects, and it cannot detect most single-gene disorders. For broader genetic risk assessment, carrier screening (a separate blood test) is recommended.

Step-by-Step: What to Expect During an NIPT DNA Test

1. Consultation: Your healthcare provider discusses NIPT as part of first-trimester screening or integrated screening options. A genetic counselor may be involved if you have risk factors.
2. Blood draw: A small blood sample is taken from your arm. No fasting or special preparation is needed.
3. Lab analysis: The lab measures the fetal fraction (the percentage of cfDNA from the placenta) – typically at least 4% is needed for accurate results. Lower fetal fraction may require a redraw.
4. Results: You receive a report indicating a low, intermediate, or high risk for each condition. A “high risk” result does not mean the baby has the condition; it means further diagnostic testing is strongly recommended.
5. Follow-up: If results are high risk, your provider will discuss confirmatory testing options such as CVS (10–13 weeks) or amniocentesis (15–20 weeks). Even with a low-risk result, remember that NIPT is a screening test and cannot guarantee a healthy baby.

NIPT vs. Other Prenatal DNA Tests

While NIPT is the most common DNA-based screening test, other tests exist for different purposes. The table below compares key options available in the United States.

Other screening tests like the first-trimester screening (combined nuchal translucency ultrasound and blood tests) and quad screen (maternal serum markers) are also used but do not analyze fetal DNA directly. Integrated screening combines first- and second-trimester results for improved accuracy. For paternity determination, a prenatal paternity test can be done via NIPT (non-invasive) or through CVS/amniocentesis, though it is not a medical screening test.

Understanding Your NIPT Results and Next Steps

It is important to discuss your NIPT results with a healthcare provider or genetic counselor. A “low risk” result is reassuring but does not rule out all problems. A “high risk” result should be followed by diagnostic testing because NIPT can have false positives, especially for rare conditions. The positive predictive value (PPV) varies by the condition and the population. For example, NIPT for Down syndrome has a PPV of over 90% in women at high risk, but lower in low-risk women. Always confirm with CVS or amniocentesis if you would consider those options.

If you are early in pregnancy and want comprehensive genetic information, many providers recommend combining NIPT with carrier screening. Carrier screening identifies if you and your partner carry genes for conditions like spinal muscular atrophy, fragile X syndrome, or cystic fibrosis. Together, these tests provide a broader picture of fetal health.

Disclaimer: This guide is for educational purposes only and does not replace medical advice. Always consult your doctor or a genetic counselor for personalized recommendations.

If you are ready to learn more about your options, you can order a comprehensive prenatal screening panel online and get results quickly, all from the comfort of your home. Our tests are reviewed by certified genetic counselors and analyzed in CLIA-certified labs.