Pre-natal diagnosis via Amniocentesis

      Genetic information about a fetus can be obtained by analysis of amniotic fluid or the shed cells in the amniotic cavity. In the amniocentesis procedure, fluid is withdrawn by means of a needle inserted through the amnion into the placental sac. Biochemical analysis of the fluid itself may indicate a genetic condition (e.g., high levels of phenylalanine may indicate PKU).  Karyotypic analysis of shed fetal cells can be used to determine gender (Barr body determination), or more specific karyotypic conditions (e.g., Down Syndrome or Trisomy-21). Direct analysis of DNA by various RFLP and PCR tests allows for much more rapid diagnosis, an important consideration in decisions about second trimester pregnancies.

    The amniocentesis procedure entail some risk of damage to the mother and/or fetus. In general, in the absence of indications of specific genetic risk from family history, amniocentesis is not recommended as a general prenatal screen.


Figure 2002 by Griffiths et al. ; text 2013 by Steven M. Carr