Cell-Free Fetal DNA
Indications for Considering the Use of Cell-Free Fetal DNA
- Maternal age 35 years or older at delivery.
- Fetal sonographic findings indicating an increased risk of aneuploidy.
- History of a prior pregnancy with a trisomy.
- Positive test result for aneuploidy, including first trimester, sequential, or integrated screen, or a quadruple screen.
- Parental balanced robertsonian translocation with increased risk for fetal trisomy 13 or 21.
- WHY TEST
- Patients at increased risk of aneuploidy can be offered testing with cell-free fetal DNA. This technology can be expected to identify approximately 98% of cases of Down syndrome with a false-positive rate of less than 0.5%.
- Cell-free fetal DNA testing should not be offered to low-risk women or women with multiple gestations because it has not been sufficiently evaluated in these groups.
- A family history should be obtained before the use of this test to determine if the patient should be offered other forms of screening or prenatal diagnosis for familial genetic disease.
- Cell-free fetal DNA testing should not be part of routine prenatal laboratory assessment, but should be an informed patient choice after pretest counseling.
- Pretest counseling should include a review that although the cell-free fetal DNA test is not a diagnostic test, it has high sensitivity and specificity. The test will only screen for the common trisomies, at the present time, gives no other genetic information about the pregnancy.
- If a fetal structural anomaly is identified on ultrasound examination, invasive prenatal diagnosis should be offered.
- Cell-free fetal DNA does not replace the accuracy and diagnostic precision of prenatal diagnosis with CVS or amniocentesis, which remain an option for women.
- A negative cell-free fetal DNA test result does not ensure an unaffected pregnancy.
- A patient with a positive test result should be referred for genetic counseling and offered invasive prenatal diagnosis for confirmation of test results.
WHO NOT TO TEST
What is Trisomy 21, 18 and 13?
Genes are the part of the a cell that contain the biological information that control the growth and development of cells. Genes, alone or in combination, determine many of the genetic traits that a person inherits, including risks of developing certain diseases or conditions. Genes are grouped into larger structures within the cells call chromosomes. The human body has 23 distinct chromosome pairs or copies. Trisomy 21,18 or 13 means there are three copies of either chromosome 21, 18 or 13, instead of two.
What is Down Syndrome?
Down syndrome is a condition in which an extra copy of chromosome 21 causes delays in the way a child develops, both mentally and physically. Not everyone with Down syndrome is affected in the same way, and there is no way to determine before birth how a child may be affected. There are three different types of Down syndrome with the most common referred to as trisomy 21. The other two types are called Robertsonian translocation and Mosaicism and these occur in about 4-6% of babies born with Down Syndrome.
Down syndrome affects about 1 in every 700 babies. The risk to have a child with Down syndrome does increase with the mother's age, but mothers of all ages can have a child with Down syndrome and it can occur in people of all races.
What is Edwards Syndrome?
Trisomy 18, also known as Edwards syndrome, is caused by an extra copy of chromosome 18. About 1 in every 5,000 babies is born with trisomy 18.
What is Patau Syndrome?
Trisomy 13, also known as Patau syndrome, is caused by an extra copy of chromosome 13. The condition is much less common than Down syndrome and occurs in about 1 in 16,000 babies born.
The American College of Obstetricians and Gynecologist (ACOG) recommends that all pregnant women be offered a screening test for fetal chromosomal abnormalities, regardless of the woman's age. Screening may be a maternal blood test done in the first trimester along with ultrasound, or it can be a maternal blood test done in the second trimester without ultrasound, or a combination of both.
ACOG also recommends that invasive diagnostic testing, such as chorionic villus sampling (CVS) or genetic amniocentesis, for aneuploidy should be made available to all women, regardless of maternal age. These surgical procedures obtain tissue/cells that allow for highly accurate diagnosis of genetic variations like trisomy 21, 18 or 13. CVS and amniocentesis are invasive and carry a small risk of causing a miscarriage.
Noninvasive Testing for Women at Increased Risk for Trisomy 21, 18 and 13
A noninvasive blood test is available for women with increased risk indicators for fetal chromosome variations. The test detects an increased amount of chromosomal 21, 18 and 13 material (mother and baby) that is circulating in your blood.The increased risk factors, include one or more of the following:
- Advanced maternal age
- Personal/family history for chromosomal abnormalities
- Fetal ultrasound abnormality suggestive of aneuploidy
- Positive serum screening test
Why is Prenatal Testing for Trisomy 21, 18 and 13 Important?
Prenatal testing for trisomy 21, 18 and 13 can help determine whether your baby has a genetic abnormality. Knowing the risk for trisomy 21, 18 and 13 can help you , your family and your health care provider make informed decisions about your pregnancy.
With your health care provider, you can prepare medically, emotionally and financially for the birth of a child with special needs, such as arranging for delivery in a medically appropriate setting.