Double, triple and quadruple marker tests
Blood tests measuring substances from the pregnancy that shift the estimated chance of chromosomal conditions. The names count how many are measured.
When: Double marker with the NT scan (11–13+6 weeks); triple and quadruple markers at 15–20 weeks
Screening test — gives a chance, not an answer
Also called: Maternal serum screening · Quad screen · Triple test
What it is
These are blood tests taken from your arm. They measure substances that come from the pregnancy and circulate in your blood, and the levels shift the estimated chance of certain chromosomal conditions up or down.
The names are just a count of how many substances are measured. Double marker measures two, triple measures three, quadruple measures four. More markers generally means a more refined estimate — which is the whole reason there is more than one version.
All of them are screening tests. Like the NT scan, they give a chance rather than an answer, and a result outside the usual range is a reason to discuss further testing rather than a finding about your baby.1
Double marker — with the NT scan
Measures two substances (free β-hCG and PAPP-A) and is done in the same 11 to 13 weeks and 6 days window as the NT scan. Combining the blood result with the nuchal measurement is what is meant by *combined first-trimester screening*, and the two together give a better estimate than either on its own.
Triple and quadruple markers — the second trimester
Taken between 15 and 20 weeks, these are the option when the first-trimester window has passed. The triple test measures three substances; the quadruple adds a fourth. They also flag a separate group of conditions affecting the spine and skull, which the first-trimester tests do not.
Why an accurate due date matters here
Every one of these substances changes level week by week through pregnancy. The result is interpreted against how many weeks along you are, so a wrong due date produces a wrong risk estimate — which is why the dating scan comes first.
What happens after a positive result
A screening result outside the usual range is not a diagnosis. The next step is a conversation about diagnostic testing, which can give a definite answer, and about what you would want to do with that answer. Nothing happens without your decision.1
No scan or screening test can rule out every condition. What each one looks at, what it found, and what it means for you is a conversation with the doctor who performed it — this page explains the tests, it does not interpret your results.
References
- American College of Obstetricians and Gynecologists Committee on Practice Bulletins—Obstetrics, Committee on Genetics, Society for Maternal-Fetal Medicine. Screening for Fetal Chromosomal Abnormalities: ACOG Practice Bulletin, Number 226. Obstetrics and Gynecology. 2020;136(4):e48-e69. PMID 32804883. doi:10.1097/AOG.0000000000004084The ACOG guideline on chromosomal screening — that every screening test gives a risk rather than a diagnosis, and that a diagnostic test is needed to confirm a positive result.
Sources are listed for the specific statements they support. They are published research and guidance, not a substitute for a consultation — what applies to you is decided by a doctor who has assessed you.