Quad Screen (Multiple Marker Screening): A Second-Trimester Prenatal Blood Test for Birth Defect Risk Assessment
A blood test during pregnancy that measures four substances in the mother's blood to assess the risk of certain chromosomal abnormalities and neural tube defects.
{"A simple blood test performed between 15-22 weeks of pregnancy","Screens for Down syndrome, Edwards syndrome, and neural tube defects","Results indicate risk level, not a definitive diagnosis"}
Key facts at a glance
- LOINC
- 49092-0
- Short code
- 2nd trimester 4 screen SerPl-Imp
- Synonyms
- 2nd trimester 4 screen SerPl-Imp
- Category
- chemistry
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Ref low
- 0
- Ref high
- 17
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Specimen volume
- 5 mL
- Stability
- Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 4–24 hours
- Order
- routine
What is the quad screen, and why is this blood test offered during the second trimester of pregnancy?
The quad screen is a blood test done during the second trimester of pregnancy (typically between 15-22 weeks). It measures four substances in the mother's blood: alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), estriol, and inhibin A. These substances are produced by the placenta and the fetus.
What does the quad screen check for, and which conditions such as Down syndrome and neural tube defects can it help identify?
The quad screen helps assess the risk of: 1) Down syndrome (trisomy 21), 2) Edwards syndrome (trisomy 18), and 3) Neural tube defects such as spina bifida or anencephaly. It is important to understand that this is a screening test, not a diagnostic test—it estimates risk rather than providing a definitive answer.
How is the quad screen test performed, and what can you expect when your blood sample is drawn?
A healthcare provider will draw a small blood sample from a vein in your arm. The sample is then sent to a laboratory for analysis. No special preparation is needed—you can eat and drink normally before the test.
Understanding Your Quad Screen Results: What a Positive or Negative Screening Result Means for You and Your Baby
Results are usually given as a probability or risk ratio (e.g., 1 in 1,000). A 'positive' screen means there is a higher risk, but does not confirm a problem. Conversely, a 'negative' or 'low-risk' result means the risk is lower, but does not completely rule out conditions. Your healthcare provider will explain your specific results and discuss whether follow-up testing is recommended.
Follow-Up Testing After an Abnormal Quad Screen: Ultrasound, Cell-Free DNA, Amniocentesis, and Other Diagnostic Options
If the quad screen shows a higher risk, your doctor may recommend additional tests for confirmation. These may include a detailed ultrasound (especially for neural tube defects) or more invasive procedures like amniocentesis, which can provide a definitive diagnosis.
Reference range
NCBI: NSE 0-17 ng/mLN/A
No special preparation usually required. Stay well hydrated. Inform your healthcare provider of all medications and supplements you are taking.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
The quad screen is a valuable tool for identifying pregnancies that may have a higher risk for certain genetic conditions and birth defects. It allows healthcare providers to offer appropriate counseling and follow-up testing to families. However, it is important to interpret results in the context of the mother's age, weight, race, and whether she has diabetes. The test has a false positive rate—meaning sometimes it suggests higher risk when the baby is actually healthy.
Frequently asked questions
Is the quad screen mandatory?
Does a positive result mean my baby has a problem?
What is the difference between screening and diagnostic tests?
Can I have the quad screen if I'm carrying twins?
When will I get my results?
Sources
- 1
- 2
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 17, 2026. · Read our editorial policy