Antenatal screening and testing can detect the likelihood of a baby being born with Down's syndrome. In the first trimester of pregnancy, down's syndrome screening tests are done using either maternal serum testing and ultrasonographic parameters. Maternal age is an important determinant of DS risk. A combined testing using a formula based on maternal age, blood markers as well as USG signs is considered most accurate.
A special type of ultrasound scan, known as nuchal translucency, measures the pocket of fluid behind the baby's neck. Babies with Down's Syndrome usually have more fluid in their neck than normal.
In the first trimester of pregnancy the PAPP-A level is, on average, low in Down's syndrome pregnancies (about half that of unaffected pregnancies), and the nuchal translucency measurement and free ß-hCG levels are, on average, high (about double that of unaffected pregnancies). It is thus possible to interpret the risk of Down's syndrome if the values of the screening test results are known
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