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03 Dec 2016 0 Comments

Prenatal Diagnostic Tests For Chromosomal Abnormalities performed using in vitro culture

Prenatal diagnostic test such as QF-PCR which gives out 99.9% accurate and rapid results  employ Chorionic villus sampling( CVS) in which a sample of chorionic villi is removed from the placenta for testing.  The chorionic sample retrieved is tested to identify chromosomal abnormalities and other inherited disorders in babies  during the pregnancy. CVS is usually retrieved between 10 and 13 weeks from your last menscycle in these tests. CVS may be chosen over amniocentesis because it can be retrieved earlier in the pregnancy.

CVS was used for the first time by Italian biologist  Giuseppe Simoni,scientific director of  Biocell Center, in 1983.This sample is mostly associated with testing for Down Syndrome, overall, CVS can also be used to detect more than 200 disorders.

  • Reasons for having a CVS:

·         Abnormal first trimester screen results

·         Increased nuchal translucency  or other abnormal ultrasound findings

·         Family history of a chromosomal abnormality or other genetic disorder.

·         Advanced maternal age (maternal age above 35). AMA is associated with an increased risk of Down's Syndrome 

           at age 35, risk is 1:400

·         Screening test are usually carried out first before deciding if diagnostic test involving CVS should be done

Recent studies have discovered that chorionic villi can be a rich source of foetal stem cells, multi-potent mesenchymal stem cells too.

  • How is Sampling Procedure Done

There are two ways to retrieve CVS: Through the cervix (called trans-cervical) and through the abdomen (trans-abdominal). The choice is based largely on where the placenta is attached to the uterus. With both methods, the procedure is performed while having an ultrasound.

Trans-cervical CVS — In the trans-cervical CVS technique, the physician inserts a small tube through the cervix into the placenta. This is done while ultrasound guides the physician.

Trans-abdominal CVS — In the trans-abdominal CVS technique, the physician inserts a needle through the abdomen into the placenta. This is also done with ultrasound to guide the physician.

The physician can usually obtain enough placental tissue the first time he or she inserts the needle or tube into the placenta. However, if there is not enough tissue, the physician may need to try again.

  • Limitation:

A small percentage (1-2%) of pregnancies have confined placental mosaicism  where some but not all of the placental cells tested in the CVS are abnormal, even though the pregnancy is unaffected. Cells from the mother can be mixed with the placental cells obtained from the CVS procedure. Occasionally if these maternal cells are not completely separated from the placental sample, this can lead to discrepancies with the results. This phenomenon is called Maternal Cell Contamination (MCC).CVS cannot detect all birth defects, thus QF-PCR uses other sampling types such as amniocentesis and foetal blood sampling . It is used for testing  chromosomal abnormalities or other specific genetic disorders only if there is family history or other reason to test.

With these latest Prenatal Diagnostic Tests that employs the use of various in-vitro samplings you can confirm the presence any medical conditions in your baby during pregnancy.

 

REF:

http://americanpregnancy.org/prenatal-testing/chorionic-villus-sampling/

http://www.uptodate.com/contents/chorionic-villus-sampling-beyond-the-basics

http://www.mayoclinic.org/tests-procedures/chorionic-villus-sampling/expert-blog/prc-20013566

 
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