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Page: Procedure
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The basic idea of the procedure is to somehow get a hold of the fetus' cells to examine the chromosomes and/or DNA from these cells in order to rule out genetic abnormalities that could lead to birth defects.
The most accessible fetal cells are in the amniotic fluid, where one would find traces of the fetus' skin and other cells that have sloughed off the fetus during its growth. Amniotic fluid is often obtained using a long syringe, guided by ultrasound. The syringe is usually inserted in to the mother's abdominal wall or at the end of the vagina, and through the uterus wall. The physician would aim for an area of the amniotic sac that is away from the fetus so to avoid stabbing it. A small amount of amniotic fluid then gets sucked out and the syringe is withdrawn. The puncture wound should close up by itself, just like any shots one would get, and the amniotic sac should then automatically replenish the liquid over a day or so.
Once the amniotic fluid is extracted, fetal cells are separated from the fluid using a centrifuge, and the lab will check the chromosomes in the cells for abnormalities. Various types of genetic testing could be done but it would be up to the individual lab doing the work to decide on the list of diseases they are able to detect and look for. They could either be cytogenetics screening or simply looking for abnormal genes. The doctor might order additional screening to look for particular genetic signature if there is family history of that particular disease. In any case, it is impossible to perform a comprehensive screening of all known human genetic diseases at this time, regardless of which lab you and your doctor chooses.
(A side effect of cytogenetic analysis is determination of the sex of the fetus with 100% accuracy, although the sex of the fetus can be discovered using the much more common and less intrusive means of examining ultrasound images.)
In addition to the fetal cells, some labs would use the remainder amniotic fluid to find indications of non-genetic diseases the fetus might have. Levels of chemical substances, (such as alpha-fetoprotein) can be measured to detect other health problems such as hydrocephalus.
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Important notice:
The content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other
qualified health provider with any questions you may have regarding a medical condition.
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