What does sequential screening involve?

Sequential screening is a two-step process used in prenatal testing for identifying the risk of certain chromosomal abnormalities, such as Down syndrome and trisomy 18. The first part involves first-trimester screening (FTS), which assesses specific markers in maternal serum and employs an ultrasound measurement of nuchal translucency.

If the results from the FTS indicate a higher risk for abnormalities, the next step is to conduct a second-trimester quad screen. This follow-up testing further evaluates serum markers and provides additional risk assessment. The sequential approach is advantageous because it allows for early detection and potential decision-making while also reducing unnecessary invasive procedures for those determined to be at low risk.

The other options do not accurately reflect the sequential screening process; for example, immediate results from amniocentesis (as in the second choice) do not align with the typical sequential screening workflow. Similarly, conducting combined first-trimester and quad results simultaneously or solely quad testing after a normal FTS misunderstands the sequential nature that distinguishes the process.