How does Down syndrome screening work?
Blood test, ultrasound, non-invasive screening: these tests estimate a risk, but they don't provide a diagnosis on their own.
First-trimester combined screening, offered between weeks 11 and 14, pairs a blood test measuring two proteins (PAPP-A and beta-hCG) with an ultrasound measurement called nuchal translucency — the thickness of a fluid-filled space at the back of the baby's neck. These results, combined with the mother's age, give a risk estimate, not a diagnosis.
Non-invasive prenatal testing (NIPT), done with a simple blood draw as early as 10 weeks, analyzes fetal DNA circulating in the mother's blood and offers markedly better accuracy than combined screening, especially for flagging a high risk of Down syndrome. It's still a screening test, though, not a definitive diagnosis.
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When a screen comes back high-risk, a diagnostic test — amniocentesis or chorionic villus sampling — may be offered to confirm or rule out the result with certainty, by directly analyzing the baby's chromosomes. These tests carry a small risk of complications and are usually discussed in detail with a genetic counselor.
Whether to have these screenings is entirely a personal choice and never mandatory. Some families prefer to know this information to prepare, others choose not to test at all; both choices are valid, and your healthcare provider can help you decide based on your own values.
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This information is general and does not replace advice from your healthcare professional (doctor, midwife, nurse, pharmacist). Every situation is unique: always check with them before making a decision. In an emergency, call 911 or your local emergency services.
