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How do prenatal screening tests differ from prenatal diagnostic tests?

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BRCA2 tumor suppressor gene on chromosome 13 — human genetic disease Photomicrograph of the *BRCA2* tumor suppressor gene on chromosome 13 of the human genome. Inactivation of this growth-regulating gene is associated with a higher risk of developing breast cancer.

Prenatal screening and diagnostic tests serve distinct roles in assessing the health of a developing fetus.

Prenatal Screening Tests

Screening tests are generally noninvasive and are used to assess the likelihood or risk that a fetus may be affected by a specific condition. These tests are often offered to all pregnant women and typically involve:12
* Maternal blood tests: Measuring levels of substances like alpha-fetoprotein (AFP), hCG, and other hormones.12
* Ultrasound imaging: Used to examine fetal anatomy or measure markers like nuchal translucency.12

Prenatal Diagnostic Tests

Diagnostic tests are used to confirm the presence or absence of a disorder when screening results indicate an increased risk. Because they require the collection of fetal cells or DNA, these procedures are often invasive and carry a higher risk of complications, including miscarriage. Common diagnostic methods include:21
* Amniocentesis: Collecting amniotic fluid containing fetal cells.12
* Chorionic villus sampling (CVS): Sampling placental tissue.12
* Percutaneous umbilical blood sampling: Collecting fetal blood from the umbilical cord.12

While diagnostic tests provide more definitive information, the decision to undergo them involves weighing the need for certainty against the potential risks to the pregnancy.12