Definition of MSAFP (maternal serum alpha-fetoprotein)

MSAFP (maternal serum alpha-fetoprotein): The presence of AFP, a plasma protein normally produced by the fetus, in the mother's blood. The MSAFP serves as the basis for some valuable tests.

AFP is manufactured principally in the fetus's liver and, also, in the fetal gastrointestinal (GI) tract and the yolk sac, a structure temporarily present during embryonic development. The level of AFP is typically high in the fetus's blood, goes down in the baby's blood after birth, and by a year of age is virtually undetectable.

During pregnancy, AFP crosses the placenta from the fetal circulation and appears in the mother's blood. The level of AFP in the mother's blood (the maternal serum AFP) provides a screening test for a number of disorders including:

  • Open neural tube defects (anencephaly and spina bifida); and
  • Down syndrome (and other chromosome abnormalities).

The maternal serum AFP (MSAFP) tends to be:

  • High with open neural tube defects such as anencephaly and spina bifida (meningomyelocele); and
  • Low with Down syndrome (trisomy 21, an extra chromosome number 21).

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