Cell Free DNA Testing

Prenatal cell free testing

What is prenatal cell free DNA testing?

It is a form of genetic screening that pregnant women can opt for, usually early in their pregnancy, around the 10th week. 

What does it involve?

As a screening test it involves the taking of a blood sample from a pregnant woman. The blood of a pregnant woman contains their unborn baby’s DNA in their bloodstream. Cell free DNA testing screens this DNA for chromosomal abnormalities. 

The body contains 46 chromosomes, with 23 pairs in each body cell. When one of these 23 pairs contains an extra copy of a chromosome it is known as trisomy. 

This screening test is considered to be low risk for Mother and baby, and at the same highly accurate. 

What can it screen for?

Cell free DNA testing can screen for chromosomal abnormalities, such as trisomy. Several genetic disorders are caused by extra chromosomes – Down syndrome is caused by an extra chromosome 21, Edwards syndrome is caused by an extra chromosome 18, and Patau syndrome is caused by chromosome 13. 

Cell free DNA testing returns a positive or negative result. A positive result is not a confirmed diagnosis of a chromosomal disorder, however it is an indication that the unborn baby may be at higher risk of being born with a chromosomal syndrome. 

It can also confirm the sex of the body, as well as the Rh blood type of the baby.

Who is cell free DNA testing recommended for?

It is generally recommended for:

-Pregnant women over the age of 35 (this is because older maternal age is recognized as a risk factor for trisomy chromosomal abnormalities)

-Pregnant women who already have a child diagnosed with a chromosomal disorder

-If an ultrasound scan during pregnancy indicates cause for screening

-If standard prenatal tests indicate possible risk for a chromosomal abnormality

The screening is not considered to be as accurate in multiple pregnancies. This is due to the DNA of more than one baby circulating in the Mother’s blood, and the screening is not able to differentiate between the two. 

Genetic counseling and cell free DNA testing?

Before embarking on prenatal genetic screening and testing, it is important to consider genetic counseling services. These important support services can help parents-be- understand more about the different types of genetic screening options, the process involved in each, and also help guide them through any results.

A positive test result from cell free DNA screening, will usually require further and more invasive genetic testing, such as amniocentesis, in order to understand if an unborn baby has a genetic syndrome or not. 

Prenatal genetic counseling can help bring clarity to what can sometimes be a complicated and stressful process during pregnancy. They are able to help parents understand all of the options available to them, and to understand more about their child’s potential genetic and general health. 


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