Prenatal screening tests
Prenatal screening tests estimate the chance that a fetus has certain conditions. ACOG notes that both screening and diagnostic testing are offered to all pregnant women, and that choosing them is your decision.
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Screening vs diagnosis
A screening test tells you the chance that the fetus has an aneuploidy (such as Down syndrome) or a few other disorders. A diagnostic test — amniocentesis or chorionic villus sampling (CVS) — tells you whether the fetus actually has certain disorders. A positive screening result means higher risk, not a diagnosis.
The screening tests
| Test | When | What it looks at |
|---|---|---|
| First-trimester screening | 10 to 13 weeks | A blood test plus an ultrasound (nuchal translucency) measuring a space at the back of the fetus’s neck |
| Quad screen (blood test) | 15 to 22 weeks | Four substances in your blood; screens for Down syndrome, trisomy 18, and neural tube defects |
| Second-trimester ultrasound | 18 to 22 weeks | Major physical defects in the brain and spine, face, abdomen, heart, and limbs |
| Combined first- and second-trimester | Results often not until the second trimester | Combines results; more accurate than a single test |
| Cell-free DNA | From 10 weeks; results in about 1 week | DNA from the placenta in your blood; screens for Down syndrome, trisomies 13 and 18, and sex-chromosome differences |
From ACOG’s patient FAQ on prenatal genetic screening tests.
What results mean
ACOG explains that results are reported as a level of risk. A positive result means the fetus is at higher risk than the general population — it does not mean the fetus definitely has the disorder. A negative result means lower risk, but does not rule it out. A positive cell-free DNA result should be followed by a diagnostic test (amniocentesis or CVS).
Other routine tests in pregnancy
Screening for genetic conditions is one part of prenatal testing. Others include early blood tests at the first visit, the glucose test for gestational diabetes, and group B strep screening at 36–37 weeks.
Common questions
- Do I have to have prenatal screening?
- No. ACOG says screening and diagnostic tests are offered to all pregnant women; whether to have them is your choice. A genetic counselor or your provider can help you decide.
- Is cell-free DNA testing a diagnosis?
- No. It is a screening test. ACOG says a positive result should be followed by a diagnostic test with amniocentesis or CVS.
Sources
- Prenatal Genetic Screening Tests (FAQ) (opens in a new tab) — American College of Obstetricians and Gynecologists
- Prenatal Testing (health topic) (opens in a new tab) — MedlinePlus, U.S. National Library of Medicine
- What happens during prenatal visits? (opens in a new tab) — Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD)
Questions about this page
Tell us if something here is unclear or a source has changed. We cannot answer questions about your own pregnancy or care — please ask your OB, midwife, or care team. National Maternal Mental Health Hotline: call or text 1-833-TLC-MAMA (1-833-852-6262). Crisis: call or text 988.
We can’t answer questions about your own diagnosis, medication, or treatment — please ask your prescriber. We also can’t book appointments, check your insurance, or refer you to a clinic.
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