TRIPLE TEST
General informations

The general approach to prenatal screening for Down`s syndrome is to estimate a woman`s risk of having an affected pregnancy on the basis of factors such as maternal age, serum concentration of various analytes, and ultrasound measurements that have been found to be associated with Down`s syndrome and are frequentelly referred to as screening markers for the disorder. Women with a risk above a specified level (> or = to 1/250) are classified as positive on screening. These women are then offered a diagnostic test either amniocentesis or chorionic villus sampling.
Down syndrome is associated with:

  1. LOW Maternal Serum Alpha-fetoprotein
  2. LOW Unconjugated Estriol concentrations
  3. HIGH Maternal Serum Human Chorionic Gonadotropin
  4. HIGH Inhibin A concentrations.

Measurements of the first three markers, in addition to age, constitute the widely used Triple test.
Measurements of all four (with age) make up the Quadruple test.
The Triple test is a second trimester screening test, but in the first trimester it is possible to search other signs that are associated with Down Syndrome:

  1. HIGH values for fetal Nuchal Traslucency
  2. HIGH maternal serum concentrations of the Free Beta subunit of Human Chorionic Gonadotropin
  3. LOW serum concentrations of Pregnancy-Associated Protein A.

Nuchal traslucency has been used either alone or in combination with the two serum markers (the combined test) in another screening protocol.

First trimester screening 85% true positive
5% false positive
at 10 to 13 weeks, based on:
nuchal traslucency
serum pregnancy-associated plasma protein A
free beta subunit of human chorionic gonadotropin
Second trimester sreening
(Double, Triple and Quadruple test)
59-76% true positive
5% false positive
at 14 to 22 weeks, based on:
serum alpha-fetoprotein
unconjugated estriol
human chorionic gonadotropin
inhibin A
Double test serum alpha-fetoprotein
human chorionic gonadotropin
Triple test serum alpha-fetoprotein
unconjugated estriol
human chorionic gonadotropin
Quadruple test serum alpha-fetoprotein
unconjugated estriol
human chorionic gonadotropin
inihibin A

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