Genetic testing – evaluating your baby’s chromosomes or genes for abnormalities – is commonly discussed at an early prenatal visit. If any of the relatives of the baby’s mother or father has genetic disorders like Down syndrome, cystic fibrosis, or sickle cell disease, among others, your healthcare provider or genetic counselor may suggest testing to determine if your baby could be affected as well. Testing options commonly include amniocentesis, chorionic villus sampling (CVS) or cell-free fetal DNA testing.
The decision to undergo genetic testing is a personal choice. To aid your decision-making process, Pregistry is providing a series of articles to provide you with an explanation of what each test is, when and why it might be recommended, and what the results mean.
This blog talks about Cell-Free Fetal DNA Testing (cfDNA).
All about Cell-Free Fetal DNA testing
During at least one prenatal visit, your healthcare provider will discuss the option of undergoing fetal genetic testing. Test options include amniocentesis, chorionic villus sampling or cell free fetal DNA testing. While most women have some idea of what an amniocentesis and chorionic villi sampling (CVS) are, not many have heard of cell-free fetal DNA testing.
Cell-free fetal DNA testing is a type of noninvasive prenatal testing used to detect fetal chromosomal abnormalities, such as trisomy 21 (Down syndrome) and other genetic disorders. It can also tell you the baby’s gender and rhesus (Rh) blood type. It is called “non-invasive” because you only need a blood test to have this test done. It does not require sampling the amniotic fluid or the placenta like amniocentesis and CVS do. Fetal cells originating from the placenta comprise approximately 3-13% the mother’s total cell-free DNA by 10 weeks gestation. The American College of Obstetricians and Gynecologists reports that cfDNA testing can be obtained by a simple blood test from 9 weeks of pregnancy through delivery.
cfDNA testing is able to detect >99% of all Down syndrome (trisomy 21) cases and other genetic defects, but it is less accurate in low risk women. It does not provide insight into the presence of neural tube or ventral wall abnormalities.
Who should and should not have cell-free DNA testing?
Currently, the cell-free DNA test is only recommended for certain women in certain situations, as in the case of women with specific risk factors. These risk factors include advanced maternal age, having other children with Down syndrome, trisomy 13 or 18, or maternal Rh negative status. If you are a carrier of an X-linked recessive disorder such as Duchenne’s muscular dystrophy or hemophilia which only affect males, it is important to note that the test cannot determine if your baby has the X- linked disorder, but will confirm its gender. If the baby is male, your genetic counselor can discuss with you additional testing that may be required.
The American College of Obstetricians and Gynecologists and the Society for Maternal–Fetal Medicine recommend cell-free DNA testing for women who have abnormal ultrasound results indicating the possibility of chromosomal abnormalities and for those women who have received abnormal first or second trimester screening results.
Women who are having a multiple pregnancy (twins or more) or who have used an egg donor to conceive, should not have the cell-free fetal DNA testing because the results may not be accurate under these circumstances.
Speak with your insurance carrier to see if the test is covered under your insurance policy.
Are there risks associated with cell-free fetal DNA testing?
Having blood drawn is, of course, a low-risk procedure. The risk with cfDNA testing is its rate of false positive results (that means the test result is wrong and the baby does not really have a genetic defect). For women who are at low risk of having babies with genetic defects, the test results are less accurate than for those at high risk. Decisions made based on erroneous test results can be devastating. Therefore, only high-risk women are advised to take this test, and if the results are positive, the diagnosis should be confirmed by amniocentesis or CVS prior to making decisions about pregnancy termination.
What do the results tell me?
The results of your genetic test will be discussed with your health care provider or genetic counselor so that, if necessary, additional testing can be recommended.
Normal results may indicate that no additional testing is necessary. However, it is important to understand that no test is 100% accurate. A negative result does not guarantee that your baby does not have a chromosomal or genetic abnormality. Discuss this possibility with your genetic counselor, especially if you are high-risk.
If the results indicate the presence of a chromosomal abnormality, amniocentesis or CVS may be recommended for confirmation. When undergoing testing because you are an X-linked recessive disorder carrier and a male fetus is confirmed, amniocentesis or CVS may be recommended for diagnosis. If you are known to be Rh negative and the fetus is confirmed to be negative as well, treatment is not indicated. However, if the fetus is confirmed to be Rh positive, and you’ve previously been sensitized (you had a previous Rh positive fetus or don’t know the Rh status of your prior pregnancies), close monitoring of your pregnancy will be recommended. It is important to speak with your healthcare provider about your specific situation and Rh status for personal recommendations on treatment.
Speak with your healthcare provider or genetic counselor if you are considering genetic testing and/or if you have additional questions regarding your options.