What Diseases Can Genetic Testing Detect During Pregnancy?

Discover which diseases genetic testing can detect during pregnancy, from NIPT to carrier screening. US-focused guide for informed prenatal decisions in 2026.

Genetic testing during pregnancy can detect a range of genetic conditions, including chromosomal abnormalities like Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), and Patau syndrome (trisomy 13), as well as microdeletions and single-gene disorders such as cystic fibrosis, spinal muscular atrophy (SMA), and fragile X syndrome. In 2026, non-invasive prenatal testing (NIPT) using cell-free DNA remains the most common first-line screening, offering high accuracy for common trisomies from as early as 10 weeks gestation. This guide explains the types of prenatal screening available to US parents, helping you understand what each test reveals and how to proceed with a comprehensive panel.

Understanding Prenatal Genetic Screening vs. Diagnostic Testing

Prenatal genetic testing falls into two categories: screening and diagnostic. Screening tests, such as NIPT, first-trimester screening, and quad screen, estimate the risk of certain conditions but do not confirm a diagnosis. Diagnostic tests, including chorionic villus sampling (CVS) and amniocentesis, provide definitive results but carry a small risk of miscarriage. US guidelines recommend offering all pregnant individuals screening options, with follow-up diagnostic testing for positive results. A genetic counselor can help interpret results and guide next steps.

Types of Prenatal Screening Tests

Non-Invasive Prenatal Testing (NIPT) with Cell-Free DNA

NIPT analyzes cell-free DNA fragments from the placenta circulating in the mother’s blood. It screens for the most common chromosomal aneuploidies:

• Trisomy 21 (Down syndrome)
• Trisomy 18 (Edwards syndrome)
• Trisomy 13 (Patau syndrome)
• Sex chromosome abnormalities (e.g., Turner syndrome, Klinefelter syndrome)
• Certain microdeletions (e.g., 22q11.2 deletion syndrome)

NIPT has a detection rate above 99% for trisomy 21 and typically reports a fetal fraction value, which must be above a threshold (usually 4%) for reliable results. It is available from about 10 weeks and is covered by most US insurers for high-risk pregnancies.

First-Trimester Screening

Combining a blood test (measuring PAPP-A and hCG) with a nuchal translucency ultrasound, this screening assesses risk for trisomies 21 and 18. It detects about 85% of Down syndrome cases with a 5% false-positive rate. It is typically performed between 11 and 14 weeks.

Quad Screen and Integrated Screening

The quad screen (second-trimester blood test measuring AFP, hCG, estriol, and inhibin A) screens for neural tube defects, trisomy 18, and trisomy 21. Integrated screening combines first- and second-trimester results for higher accuracy. These are less commonly used since NIPT became widely available but remain options for those who cannot access NIPT.

Carrier Screening for Single-Gene Disorders

Carrier screening tests parents for recessive genetic conditions they might unknowingly carry. If both parents are carriers, the baby has a 25% chance of being affected. Common disorders screened in the US include:

Carrier screening can be done before or during pregnancy, often via a blood draw or saliva sample. The American College of Obstetricians and Gynecologists recommends offering carrier screening for cystic fibrosis and SMA to all pregnant individuals, with expanded panels available.

Diagnostic Tests for Confirmation

Chorionic Villus Sampling (CVS)

CVS involves taking a small sample of placental tissue, usually between 10 and 13 weeks. It can diagnose chromosomal abnormalities and some genetic disorders detected by carrier screening. The procedure carries a miscarriage risk of roughly 1 in 300 to 1 in 500.

Amniocentesis

Amniocentesis extracts amniotic fluid after 15 weeks. It provides similar diagnostic accuracy as CVS but can also detect neural tube defects. The miscarriage risk is lower, about 1 in 500 to 1 in 1000. Both procedures require a referral and are typically performed after a positive screening result or for advanced maternal age.

Special Considerations: Prenatal Paternity Test and Fetal Fraction

Prenatal paternity testing can be performed using cell-free DNA from the mother’s blood as early as 7 weeks, but it is not a medical screening test and is often not covered by insurance. Fetal fraction—the proportion of cell-free DNA from the placenta—is critical for NIPT accuracy. Low fetal fraction (below 4%) may lead to a no-call result, requiring a redraw or alternative testing.

How to Choose the Right Test

Discussing your options with a genetic counselor is key. They can help you understand the detection rates, limitations, and implications of each test based on your family history, ethnicity, and gestational age. Many US labs offer comprehensive panels combining NIPT and carrier screening for a broader assessment.

To take the next step, you can order a prenatal screening panel online and receive your results within 5–10 business days, with confidential support from a genetic counselor if needed. This guide is for educational purposes only and does not replace medical advice; always consult your healthcare provider before making decisions about prenatal testing.