• Prenatal Genetic Screening: Invasive and Non-invasive Procedures

    Posted on September 30, 2013 by in Uncategorized

    Prenatal Genetic Screening

    Prenatal genetic testing is often a routine measure that many pregnant women undergo so as to determine whether the unborn child has any predisposition to a genetic illness. Women who conceive in their mid 30s and later are encouraged all the more to undergo certain tests. Some procedures are non invasive (such as an ultrasound) and other are invasive (such as amniocentesis).

    An ultrasound can for example, indicates to a good obstetrician that an unborn child might be born with Down’s syndrome by looking at the folds and creases on the neck (nuchal translucency thickness) but actual genetic tests will then be needed to establish this with more certainty; for this latter case, invasive sampling procedures are required which might include amniocentesis or chorionic villus sampling. These invasive tests are also used for prenatal paternity testing.

    Prenatal Genetic Screening for disease

    Both amniocentesis and CVS are used not only for prenatal paternity testing but also to screen unborn babies to determine whether they could be carriers of any genetic illnesses; these are however considered diagnostic tests and are carried out after more routine tests such as ultrasounds. Firstly, a pregnant woman would carry out ultrasounds or maternal serum tests. Diagnostic prenatal tests are normally only carried out following standard screening tests such as the ultrasound or the maternal serum test. In many countries this is a routine procedure though in much the same vane as prenatal paternity testing, certain ethical implications arise and from an ethical standpoint the use of this type of test for such purposes is questionable as it might be the determining factor in deciding whether to abort the child.

    Why carry out Prenatal Genetic Testing ?

    Prenatal genetic testing is done to find whether the unborn child might be suffering from any of the following illnesses (the list provided is not in any way exhaustive):

    • Down’s syndrome: sometimes also known as Trisomy 21. The condition is characterized by an extra chromosome 21. People with this condition have an extra copy of the genetic information on chromosome 21. They have slow mental capabilities and are impaired in their physical growth. Small ears, upward slant of the eyes and flat faces are typical characteristics of children with Down’s syndrome. Males with Down syndrome are in most cases infertile.
    • Turner’s syndrome: This syndrome is specific to females and is never developed by males. Females with this syndrome only have 1 X chromosome or sometimes a partial chromosome. One of the main features is stunted growth; girls can only reach a height just above 4 foot tall. Growth hormones can however be given in puberty to encourage growth. Ovaries are also impaired from proper development which affects the sufferer’s ability to develop sexually or have children.
    • Fragile X syndrome: often suffers, both male and female, have impaired cognitive abilities which in some cases can be very severe. Boys tend to be more affected then girls. Often, they are very effeminate, exhibit autistic behaviors such as wrist flopping and self talk. They often have large ears and develop large testicles in puberty.
    • Rare inherited metabolic disorders: These disorders are caused by chemical imbalances in the body. For example, Acute intermittent porphyria.

    Prenatal screening will not necessarily tell you that the unborn child has the disorder but it will tell you that it stands a chance of being born with that disorder. Once it is established that the baby has a risk of Down’s syndrome or another genetic illness, further diagnostic tests (such as CVS or amniocentesis) can be pursued.

    To be mentioned that in many countries prenatal genetic testing for diseases is standard for most women. CVS and Amniocentesis can be used to trace chromosomal abnormalities and other genetic disorders that the child might be carrying.

    Non-Invasive Prenatal Testing

    In non invasive prenatal testing fetal cells from the placenta can be isolated from a sample of the mother’s blood. For many years scientists have known that fetal cells are present in the mother’s blood but have been unable to isolate the cells because of their small numbers. The extraction for non invasive prenatal screening can only take place after the 7th week of pregnancy. It is still a relatively new field of research but conditions such as Down’s syndrome can be effectively detected with this test.

    Non invasive prenatal paternity testing is also an emerging area of study. The success rate of this test has not however, been consistent. It is nevertheless, a huge leap from invasive prenatal testing such as Chorionic Villus sampling and Amniocentesis which carry certain risks to the unborn child and mother. Non invasive testing for paternity is almost risk free; the only risk being infection at the point of venepuncture (a minor risk associated with any injection) .

    Prenatal genetic screening is often recommended for pregnant woman over the age of 35 or parents who have a history of genetic illness.

    Genetic DNA testing can also be used in the case of a boy or girl gender prediction test to discover the sex of your unborn child … read more…