What is the quad (quadruple) marker test?
In short
- The quad marker test is a blood test that measures four substances to screen for Down's syndrome, Edwards' syndrome and neural tube defects.
- It's usually done between 15 and 22 weeks, later than the first-trimester double marker or combined test.
- It gives you a chance, not a yes/no diagnosis.
- Your doctor will explain your result and any further, diagnostic tests available.
What happens
- A blood sample is taken from your arm, between 15 and 22 weeks.
- The lab measures four substances in your blood and combines the results with your age and stage of pregnancy.
- You get back a chance figure, for example 1 in 500.
The details: numbers and where they differ
The numbers
| Measure | Value | Source |
|---|---|---|
| Quad marker screening window (pregnant women (ACOG, US)) | 15–22 weeks gestation | American College of Obstetricians and Gynecologists (ACOG) |
When to call your doctor
- If you're not sure whether you've been offered this test or when it's scheduled.
- If your result comes back higher chance and you want to discuss further, diagnostic testing.
Discuss your results with your doctor: this page reports what these sources say, not advice for your situation.
Sources
- American College of Obstetricians and Gynecologists (ACOG), Prenatal Genetic Screening Tests (Patient FAQ). Named as the guideline this section describes; its text and tables are not reproduced here (All rights reserved (cite only)). Describes the quad (quadruple) blood test as measuring four substances, screening for Down syndrome, Edwards syndrome (trisomy 18) and neural tube defects, done between 15 and 22 weeks.
Sources checked 2026-09-26. How we source and check every page.
Educational summary of named sources, not medical advice.