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Maternal Serum Screening

Down Syndrome, Trisomy 18 and Neural Tube Defects



Sequential Screening

Slide 15

March 2011

Sequential screening is a type of cross trimester screening that has been introduced as a mean to increase the detection rate and provide the lowest false-positive rate. The markers used in the risk calculation include: NT and PAPP-A which are measured during the first trimester and AFP, unconjugated estriol, hCG and inhibin A which are measured in the second trimester.

In sequential screening, once NT and PAPP-A information is available, a risk calculation is performed. If the screen is positive, results are reported and this is considered the end of the screening test. In contrast, if the screen is negative, a second sample is collected in the second trimester and new risk estimate is generated.

Sequential Screening

 


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