HomeLab TestsDown Syndrome Tests
Back to Lab Tests
Down Syndrome Tests
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Lab Tests

Down Syndrome Tests

Down syndrome tests are used during pregnancy or after birth to determine if a fetus or infant has Down syndrome, a chromosome disorder caused by an extra copy of chromosome 21.

Overview

Down syndrome is a chromosome disorder. Normally, humans are born with 46 chromosomes grouped into 23 pairs. Most people with Down syndrome have an extra copy of chromosome 21, a condition known as trisomy 21. Other, less common types include translocation Down syndrome and mosaic Down syndrome.

The condition affects brain and body development, potentially causing learning, thinking, and physical health challenges. Physical signs may include a flat face, upward-slanting eyes, a short neck, and poor muscle tone.

Types of Tests

Screening Tests

These tests estimate the chance that a fetus has Down syndrome but cannot provide a diagnosis. They are safe and simple, involving blood samples and ultrasounds:

  • First trimester screening (weeks 10-13): Combines a blood test (checking markers like PAPP-A and hCG) and an ultrasound to measure fluid thickness behind the fetus's neck.
  • Second trimester screening (weeks 15-20): Known as the "quad screen," it checks levels of four substances in the blood: AFP, hCG, estriol, and inhibin A.
  • Combined or integrated screening: Uses results from both trimesters for a clearer risk estimate.
  • Cell-free DNA (cfDNA) or noninvasive prenatal screening (NIPS): Checks fetal DNA in the mother's blood. It is the most accurate screening test and can be performed as early as 10 weeks.

Diagnostic Tests

These confirm the presence of Down syndrome by examining fetal cells or DNA:

  • Amniocentesis (weeks 15-20): Collects amniotic fluid containing fetal cells.
  • Chorionic Villus Sampling (CVS) (weeks 10-13): Collects tissue from the placenta.
  • Percutaneous Umbilical Blood Sampling (PUBS): Removes a blood sample from the umbilical cord; used only when other tests are inconclusive due to higher risks.

Why do I need a Down syndrome test?

Medical researchers recommend that all pregnant individuals be offered screening. Diagnostic testing may be recommended if you are at higher risk, which includes:

  • Being age 35 or older at the time of pregnancy.
  • Having a previous child or pregnancy with Down syndrome.
  • Having a family history of Down syndrome.
  • Ultrasound findings that suggest a possible sign of the condition.

What do the results mean?

  • Positive screening result: The chance of having a baby with Down syndrome is higher than average, but it does not confirm the condition.
  • Negative/normal screening result: It is unlikely the baby has Down syndrome, though screening cannot guarantee this.

Diagnostic tests can confirm a diagnosis but cannot predict the severity of the condition's impact on the child's health and abilities.

Frequently Asked Questions

Screening tests (first‑trimester blood + nuchal translucency ultrasound, quad screen, cfDNA) estimate the probability of trisomy 21 but do not give a definitive answer. They are non‑invasive, have no miscarriage risk, and are usually offered to all pregnant people. Diagnostic tests (CVS or amniocentesis) examine fetal cells directly, providing a definitive diagnosis, but they carry a small risk of miscarriage (≈0.5‑1 %). Choose screening first to gauge risk; if the risk is high or you need certainty for decision‑making, discuss diagnostic testing with your provider.
cfDNA has a detection rate >99 % for Down syndrome with a false‑positive rate of about 0.1‑0.2 %. A negative result is highly reassuring, but a positive result is still considered a screening outcome. Because no test is 100 % certain, most clinicians recommend confirming a positive cfDNA result with CVS (10‑13 weeks) or amniocentesis (15‑20 weeks) before making irreversible decisions.
Both procedures involve inserting a needle through the abdomen; CVS samples placental tissue earlier (10‑13 weeks) while amniocentesis samples amniotic fluid later (15‑20 weeks). CVS carries a slightly higher early‑pregnancy loss risk (≈1 %) and a small chance of limb‑defect anomalies if done before 10 weeks. Amniocentesis has a miscarriage risk of about 0.5‑0.7 % and is generally considered safer for later gestational ages. Decision factors include timing of results you need, personal risk tolerance, and any contraindications (e.g., uterine anomalies).
Most blood‑based screens require you to be fasting for 8‑12 hours (especially the quad screen). Ultrasound components need a full bladder, so you’ll be asked to drink water beforehand. After the test, you’ll receive a risk ratio (e.g., 1 in 250). This number reflects the chance your baby has Down syndrome compared to the general population. A low‑risk result (often 1 in 100) prompts a discussion about diagnostic testing. Always review the numbers with your obstetrician or genetic counselor, who can place them in the context of your age, family history, and personal values.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

kontakt@hittavard.se

Ⓒ 2024. Alla rättigheter förbehålls av juxt ab

Sök
Om ossVillkor och policyVanliga frågorKontakta oss