Fetal Assessment - Invasive Techniques
Posted on August 21, 2007
Filed Under Pregnancy |
Invasive techniques for fetal assessment are reserved for pregnancies in which there is a reason to suspect an abnormality. This is because any “invasion” of the uterine cavity carries a risk to the pregnancy or the fetus.Invasive techniques allow direct analysis of fetal cells. These may come from the chorionic villi, the amniotic fluid, or a specimen of fetal blood or even skin. These techniques can detect all chromosomal abnormalities but only selected genetic defects or diseases. In general, the genetic conditions looked for are those for which there is a high level of suspicion in a particular fetus.
Invasive techniques, including amniocentesis, may be appropriate in the following situations -
• Women 35 years of age and older. This designation as high risk for a fetal defect is somewhat arbitrary, but 35 is the age at which the risk to the pregnancy of amniocentesis is approximately equal to the risk of having a baby with a trisomy, the most common of the chromosomal abnormalities. Both risks are about 1 in 200 at this maternal age. Some experts recommend testing when the father is 44 years or older, although a link between father’s age and Down syndrome has not been shown routinely.
• Parents who have had a child with Down syndrome or another chromosomal abnormality.
• Parents who are known carriers of a chromosome rearrangement, such as a translocation.
• Parents who have a family history of a genetic condition for which testing is available. A few of the more common ones are shown in the box below, although there are over 60 metabolic diseases that invasive testing is able to detect.
• Exposure to a teratogen, like certain medications, early in pregnancy that might increase the risk of an open neural tube defect, such as spina bifida.
• An elevated MSAFP or triple screen result indicating an increased risk for a neural tube defect or other condition, including a trisomy. As the mother’s blood levels are measured at or after week 15 of pregnancy, an amniocentesis, not CVS, is the appropriate follow-up test.
• Parents who are first cousins (called consanguinity).
• History of unexplained stillbirths or multiple miscarriages .
Tags:amniocentesis, chorionic villi, chromosomal abnormalities, chromosomal abnormality, diseases, down syndrome, fetus, genetic conditions, invasive techniques, neural tube defect, parents, Pregnancy teratogen
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