What is the role of prenatal screening in the diagnosis of Down syndrome?

Updated: May 18, 2020
  • Author: Gratias Tom Mundakel, MBBS, DCH; Chief Editor: Maria Descartes, MD  more...
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Prenatal screening using a combination of maternal serum biomarkers and ultrasonography can detect up to 95% of pregnancies affected by Down syndrome. [82, 83, 84, 85, 86] The false positive rate is 5%. Recently updated guidelines from the American College of Obstetricians and Gynecologists [15] state the following: (1) all women should be offered screening for aneuploidy before 20 weeks' gestation and (2) all pregnant women, regardless of their age, should have the option of diagnostic testing.

The first prenatal diagnosis of Down syndrome was made in 1968, and screening women with amniocentesis on the basis of advanced maternal age was gradually introduced into medical practice. Low maternal serum alpha fetoprotein (MSAFP) levels were associated with Down syndrome in 1983. Later, elevated human chorionic gonadotropin (hCG) and low unconjugated estriol (uE3) levels were found to be markers for Down syndrome. More recently, elevated inhibin A levels (in the second trimester) and reduced pregnancy-associated plasma protein A (PAPP-A) levels (in the first trimester) have been used to screen for Down syndrome in pregnancy. Maternal serum biomarkers can also be used to detect nonstandard trisomy 21 (translocations and mosaicism); however, detection rates for low-level mosaicism may be low. [87]

A substantial proportion of pregnancies are terminated after a prenatal diagnosis of Down syndrome. [88]

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