What is the difference between a quad screen and NIPT?

The quad screen measures four biochemical markers in maternal blood to assess risk for neural tube defects and chromosomal conditions like Down syndrome. NIPT (non-invasive prenatal testing) analyzes cell-free fetal DNA and offers higher accuracy for detecting trisomies 21, 18, and 13, but it does not detect neural tube defects. Many women choose both tests for comprehensive screening.

What is the difference between a quad screen and NIPT?

The quad screen measures four biochemical markers in maternal blood to assess risk for neural tube defects and chromosomal conditions like Down syndrome. NIPT (non-invasive prenatal testing) analyzes cell-free fetal DNA and offers higher accuracy for detecting trisomies 21, 18, and 13, but it does not detect neural tube defects. Many women choose both tests for comprehensive screening.

What Is a Quad Screen Test for Pregnancy?

Learn what the quad screen test for pregnancy is, how it differs from NIPT and carrier screening, and why US moms choose it. Comprehensive prenatal screening guide 2026.

The quad screen test for pregnancy is a maternal blood test performed between weeks 15 and 22 that measures four specific substances to assess the risk of certain fetal chromosomal conditions and neural tube defects. It is a standard second-trimester screening option in the United States, often used alongside first-trimester screening or as part of integrated screening protocols. Unlike non-invasive prenatal testing (NIPT) which analyzes cell-free DNA, the quad screen evaluates biochemical markers produced by the placenta and fetus.

Understanding the Quad Screen Test

What Does the Quad Screen Measure?

The test measures four markers in the mother's blood:

Alpha-fetoprotein (AFP) – produced by the fetal liver; elevated levels may indicate neural tube defects, while low levels can be associated with Down syndrome.
Human chorionic gonadotropin (hCG) – a placental hormone; abnormal levels may suggest chromosomal abnormalities.
Unconjugated estriol (uE3) – produced by the placenta and fetal adrenal glands; low levels are linked to Down syndrome and Edwards syndrome.
Inhibin A – a placental hormone; elevated levels can indicate Down syndrome.

When Is It Done and How?

The quad screen is typically performed between 15 and 22 weeks of pregnancy. A blood sample is drawn from the mother's arm and sent to a laboratory. Results are usually available within a week. This test is not diagnostic; it only provides a risk estimate. If results show increased risk, a genetic counselor may recommend diagnostic procedures such as chorionic villus sampling (CVS) or amniocentesis for confirmation.

Quad Screen vs. Other Prenatal Screenings

Pregnant women in the US have several screening options. The table below highlights key differences:

Test Type	Timing	What It Detects	Key Feature
Quad Screen	15–22 weeks	Neural tube defects, Down syndrome, Edwards syndrome	Second-trimester blood test; measures four markers
First-Trimester Screening	11–14 weeks	Down syndrome, Edwards syndrome	Combines blood test and nuchal translucency ultrasound
NIPT (Non-Invasive Prenatal Testing)	From 10 weeks	Down syndrome, Edwards syndrome, Patau syndrome, sex chromosome conditions	Analyzes cell-free fetal DNA; high accuracy
Carrier Screening	Before or during pregnancy	Genetic conditions like cystic fibrosis, spinal muscular atrophy, fragile X syndrome	Checks if parents carry recessive gene mutations

Integrated screening combines first-trimester and quad screen results for a more comprehensive risk assessment. Many US providers now offer NIPT as a primary screen, but the quad screen remains valuable for detecting neural tube defects, which NIPT cannot identify.

What Do Results Mean?

A “positive” or “screen-positive” result indicates an increased risk, not a diagnosis. The fetal fraction (proportion of cell-free DNA from the placenta) is not measured in quad screens, but it is a key factor in NIPT. If the quad screen suggests elevated risk, a genetic counselor can discuss options like targeted ultrasound, CVS, or amniocentesis. Most women with screen-positive results go on to have healthy babies.

Next Steps After Quad Screen

Discuss results with your healthcare provider or a genetic counselor.
Consider follow-up diagnostic testing if risk is elevated.
If you have not already done so, carrier screening for conditions like spinal muscular atrophy, fragile X syndrome, and cystic fibrosis can provide additional information about your baby's health.

Integrating Quad Screen with Comprehensive Prenatal Screening

Many expectant parents choose to combine the quad screen with NIPT and carrier screening to get a fuller picture of fetal health. While the quad screen addresses structural and chromosomal risks, NIPT offers high accuracy for common trisomies, and carrier screening identifies inherited disorders. Together, these tests form a robust prenatal screening panel. If you are considering a prenatal paternity test, note that it is a separate DNA analysis and not part of routine screening.

Disclaimer: This content is for educational purposes only and does not constitute medical advice. Always consult your healthcare provider for personal prenatal care decisions.

Ready to take the next step? You can easily order a prenatal screening panel online from a trusted US laboratory and receive results quickly, giving you peace of mind during your pregnancy.