An Introduction to Amniocentesis

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Amniocentesis is a prenatal procedure where amniotic fluid is drawn from the mother in the second trimester (16 weeks+) for genetic testing. There are a few types of genetic tests that can be done on the amniotic fluid including a karyotype, fluorescent in situ hybridization (FISH), microarray analysis, and testing for a specific genetic disease.

  • Karyotype: Shows a picture of the chromosomes in a single cell, which allows identification of a chromosome condition such as Down syndrome as well as the predicted genetic sex of the fetus.
  • FISH: Applies dye that attaches to certain chromosomes, also allowing the patient to know the predicted genetic sex of the baby, and also how many copies of chromosomes 21, 18, 13, X and Y are present.
  • Microarray: More detailed molecular karyotype, which tells you how many copies of each chromosome there are, and whether or not those chromosomes have any deletions or extra pieces, as well as revealing the predicted genetic sex of the fetus.
  • Analysis for specific genetic conditions takes about 1-3 weeks and requires a maternal blood sample in addition to the fetal sample.

Some things to consider when deciding to do an amniocentesis is that 0.1-0.3 of patients who have had an amniocentesis go on to have a miscarriage. Results are received in the second trimester, so that may impact the option for pregnancy termination. Additionally, amniocentesis can be done in the third trimester for delivery planning.

Finally, if maternity care coverage is included in your health insurance, both the amniocentesis and genetic testing are likely to be included (although, the genetic testing may require pre-authorizations). If it is not included, these tests can be costly in the United States: $1,000 for a karyotype, $1,200 for a FISH, $3,000 for a microarray, and about $500-$2,000 for genetic testing for a specific genetic condition. In countries with nationalized healthcare, such as the United Kingdom, amniocentesis may be covered.

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This project is sponsored by Myriad Genetics.

Master List

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To date, there have been hundreds of X-linked conditions identified—many of them only affecting a few people around the world. While all X-linked conditions are caused by mutations on the X chromosome, each condition is different and has a unique set of symptoms.

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