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Fetal DNA Testing

Fetal DNA TestingIn late 2011, a new method of fetal genetic testing was introduced. Called cell-free fetal DNA testing or non-invasive prenatal testing (NIPT), this testing uses maternal blood to test for abnormalities in the fetal DNA. First introduced to detect Down syndrome (trisomy 21), the test is now also used to detect the less common trisomies 18 and 13 as well as other conditions.  This type of test is offered by several different companies that each have their own brand name for the test.

We offer NIPT to all women at increased risks for the designated conditions.  Those in the high-risk group include women over the age of 35, someone with a blood test result or ultrasound marker associated with a chromosome abnormality, and anyone with a family history or previous pregnancy with a history of one of these conditions.

The fetal DNA test

The cell-free fetal DNA test/NIPT can be performed after the tenth week of pregnancy. A small amount of blood is drawn from the mother’s arm. In that blood sample are small amounts of  DNA that have been released from placental cells into the woman’s bloodstream.

If the test results come back positive, it does not mean the baby has that condition.  A more definitive diagnostic procedure (such as an amniocentesis) is recommended. Studies on the cell-free fetal DNA tests have shown that they are ~99 percent sensitive in detecting Down syndrome with a less than 1 percent false positive rate. Previously available non-invasive tests had considerably higher false positive results, which led to more recommendations for further testing and more worry for the parents.

Other fetal testing

Before the introduction of cell-free fetal DNA testing, at-risk women only had the options of traditional serum screening or invasive diagnostic procedures such as amniocentesis.  Amniocentesis is done to provide definitive information regarding chromosome abnormalities and can also be used to test for many other conditions.  However, because the amniocentesis involves using a fine needle to remove a small amount of fluid surrounding the fetus,  the procedure carries a small risk of miscarriage. Some women still choose to have an amniocentesis and we recommend it particularly for women who have a high-risk finding on the fetal DNA test, certain fetal abnormalities identified on ultrasound, or family history of particular genetic syndromes.

Another test that may be performed in conjunction with NIPT is the nuchal translucency screening, which is a measurement of the fluid collection at the back of the neck done as part of an ultrasound between 11 and 14 weeks gestation. This is a general screening tool that may reveal an increased risk for a fetal cardiac defect or higher risk for other type of defects in addition to raising suspicion for chromosome abnormalities.  Findings from the nuchal translucency screening may lead to the recommendation for other diagnostic testing.

Fetal DNA testing costs

Costs for fetal DNA testing vary greatly based on each individual’s insurance and levels of coverage are constantly evolving. The U-M Fetal Diagnostic Center team recommends patients inquire with the laboratory to clarify expected cost of the test.

The fetal consultation

As with all genetic testing, meeting with a qualified genetic counselor is important so you can understand the test and its results. The genetic counselor will explain any further testing that may be recommended and any treatment or follow-up options that are available.

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Audrey Norby, MS, CGC, genetic counselorAudrey Norby, MS, CGC, is a 2009 graduate of the Indiana University Genetic Counseling Program. Following graduate training, she joined the team of genetic counselors at the U-M Fetal Diagnostic Center during the summer of 2009.

 

 

university of michigan women's hospitalUniversity of Michigan Von Voigtlander Women’s Hospital opened in December 2011, offering women a state-of-the-art place to welcome their babies to the world in the most caring and comfortable way possible.  From private rooms to birthing tubs, each feature was designed around mom and baby’s every need.  Learn more at www.UofMhealth.org/birthcenter.