What is included in second-semester prenatal screening of Down syndrome?

Updated: May 18, 2020
  • Author: Gratias Tom Mundakel, MBBS, DCH; Chief Editor: Maria Descartes, MD  more...
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Tests used for second-trimester screening include the triple and quadruple screens. The triple screen measures serum hCG, AFP and unconjugated estriol to calculate the risk of Down syndrome and can detect up to 69% of Down syndrome pregnancies. Currently, the quadruple test, usually performed at 15-18 weeks' gestation, is the most common screening test performed in the second trimester. This screen measures inhibin A in addition to the biochemical markers measured in the triple screen and provides an 81% detection rate for Down syndrome. In addition, the quadruple test serves as a screening test for open neural tube defects (since it involves measurement of AFP) and can also detect trisomy 18.

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