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Genetic Screening

Chromosomal abnormalities account for nearly 15% of mid-trimester pregnancy losses . Fortunately, there exists for all pregnant women an opportunity for a comprehensive prenatal evaluation of their fetus for the purpose of determining genetic and morphologic (structural) normalcy.
Although it is not considered mandatory or routine, women at risk for fetal problems may avail themselves of several testing procedures as well as be offered screening procedures . Examples of these procedures include: amniocentesis ; CVS ; fetal blood sampling; blood screening ; high resolution ultrasound and direct fetal visualization via fetoscopy.

Because some of these tests are invasive it is important for the patient and her physician to have a clear understanding of what information is to be ascertained from a particular test, its risks and its limitations. With these guidelines well defined, the prenatal diagnosis of fetal abnormalities becomes an important tool in the contemporary care of pregnancy.  

Pre-pregnancy counseling or is very important, and women should consult their physician or other primary caregiver prior to conception, or at least very early in the first trimester, so as to determine any risk factors for genetic diseases; e.g. familial disorders such as cystic fibrosis, muscular dystrophy, hemophilia, sickle cell anemia, Tay-Sachs Disease or chromosomal disorders, the most common being Downs Syndrome or Trisomy 21.  

Carrier states can then be detected prior to conception or early in the pregnancy. Appropriate diagnostic tools may be utilized as described above: blood sampling, chorionic villus sampling, amniocentesis and high resolution ultrasound. For families who have been identified at risk for these or other hereditary diseases, genetic counseling is indicated.

For families not at risk for genetic disorders , certain screening tests (non-invasive) are available.
The maternal Alpha-Feto Protein test (now combined with two other markers-HCG and Estriol) is a screening test primarily for two particular classes of disorders; neural tube defects (NTD) and chromosome abnormalities, the most common being Downs Syndrome or Trisomy 21. If the test should return as positive , either above or below the limits of the mean, it does not necessarily indicate there is a problem-only that their might be a higher risk for a problem. The next procedural step would be to perform a detailed ultrasound exam, sometimes called a level 2 scan and possibly an amniocentesis . These second line tests can better define the health of the fetus within the limitations of each test.  

Genetic testing today, although available now for many years, is on the cusp of a new frontier-that of very early, embryonic diagnosis via micro-fetal blood sampling and maternal blood sampling for fetal cells and fetal chromosome analysis. Early fetal treatment may also be possible through current and ongoing research in gene manipulation and therapy.  

For further, more detailed information on this topic, please refer to the reference source for this page.

The information in this page is presented in summarised form and has been taken from the following source(s):
1. Hygeia Foundation : http://hygeia.org/


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  http://www.hon.ch/Dossier/MotherChild/birth_disorders/genetic_screening.html Last modified: Jun 24 2002