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What is the Quad Screen?

The quad screen is a blood test done during the second trimester of pregnancy (typically between 15-22 weeks). It measures four substances in the mother's blood: alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), estriol, and inhibin A. These substances are produced by the placenta and the fetus.

What Does This Test Check For?

The quad screen helps assess the risk of: 1) Down syndrome (trisomy 21), 2) Edwards syndrome (trisomy 18), and 3) Neural tube defects such as spina bifida or anencephaly. It is important to understand that this is a screening test, not a diagnostic test—it estimates risk rather than providing a definitive answer.

How is the Test Performed?

A healthcare provider will draw a small blood sample from a vein in your arm. The sample is then sent to a laboratory for analysis. No special preparation is needed—you can eat and drink normally before the test.

Understanding Your Results

Results are usually given as a probability or risk ratio (e.g., 1 in 1,000). A 'positive' screen means there is a higher risk, but does not confirm a problem. Conversely, a 'negative' or 'low-risk' result means the risk is lower, but does not completely rule out conditions. Your healthcare provider will explain your specific results and discuss whether follow-up testing is recommended.

Follow-up Testing

If the quad screen shows a higher risk, your doctor may recommend additional tests for confirmation. These may include a detailed ultrasound (especially for neural tube defects) or more invasive procedures like amniocentesis, which can provide a definitive diagnosis.