Prenatal screening

Prenatal screening uses tests during pregnancy to estimate the chance of particular fetal conditions. A screening result indicates risk rather than establishing a diagnosis.

First-trimester screening: A pregnancy screening approach combining maternal blood tests and ultrasound findings to estimate the chance of certain fetal conditions. It illustrates how biochemical markers and ultrasound measurements can contribute to one risk estimate.
Prevalence: The proportion of a population that has a condition at a given time or over a specified period. Condition prevalence affects how likely a positive screening result is to be a true positive.
Down syndrome screening: Prenatal tests that estimate the chance a fetus has trisomy 21. It is a common application of screening, with both blood-based and DNA-based options.
Amniocentesis: A procedure that samples amniotic fluid, often to diagnose genetic or chromosomal conditions. Unlike screening, it can provide diagnostic evidence, though it is invasive.
Cell-free fetal DNA testing: A blood test that analyzes placental DNA fragments circulating in a pregnant person's bloodstream to screen for selected chromosome conditions. It screens through DNA analysis and often detects common chromosome conditions more accurately than earlier blood-test methods.
Gestational age: The duration of pregnancy, usually measured from the first day of the last menstrual period. Screening options and the interpretation of results depend on when in pregnancy testing occurs.
Edwards syndrome: A chromosome condition caused by an extra copy of chromosome 18. It is among the conditions included in several prenatal chromosome-screening tests.
Chorionic villus sampling: A prenatal procedure that samples placental tissue to test for genetic or chromosomal conditions. It is an invasive diagnostic option that may follow a concerning screening result.
Nuchal translucency: An ultrasound measurement of fluid behind the fetal neck, used in early pregnancy screening. This measurement can contribute to risk estimates for chromosome conditions and some structural abnormalities.
Diagnostic test: A test intended to determine whether a particular condition is present, rather than estimate its probability. It clarifies the distinction between a screening result and confirmation of a condition.

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