Choosing the right prenatal testing for you and your baby can be confusing, especially with the many new options available to you today.
Historically, there have been both screening and diagnostic tests that check for abnormal chromosomes. These chromosomes may result in conditions such as Down syndrome or other more rare genetic abnormalities that can affect your baby’s health.
A screening test determines how high a chance there is of having a problem, but does not give a definitive yes or no result. Invasive diagnostic tests — which include amniocentesis and chorionic villus sampling (CVS) — are definitive, but come at some risk to the pregnancy.
A new option called cell-free DNA testing may provide answers without risk to the pregnancy. Diagnostic tests such as CVS and amniocentesis provide a definitive answer to questions about your baby’s health. However, the more accurate information comes at the expense of an invasive procedure that carries a small risk to the pregnancy, including damage to the fetus and miscarriage.
Early risk assessment is a screening test that examines hormones in your blood and the thickness of your baby’s neck fold on ultrasound to estimate whether or not Down syndrome affects your baby. The results of the test will give you a risk such as 1 in 1,000 that your baby is affected by a chromosomal abnormality. Because such testing consists of a simple blood test and an ultrasound, it has no risk of pregnancy loss.
CELL-FREE DNA TESTING
Cell-free DNA testing may be changing the traditional options, offering expectant parents more information than was available previously through traditional screening tests, without the risks associated with traditional invasive diagnostic tests. Using DNA from the pregnancy that circulates through your blood, a simple maternal blood test may be able to tell you about your baby’s chromosomes without any risk to the fetus. This would give you and your family information about Down syndrome, as well as other fetal chromosomal abnormalities such as Trisomy 13 and 18.
Many cell-free DNA tests can reveal your baby’s gender before it’s even visible on an ultrasound, which may be important if there is a concern about a sex-linked genetic abnormality. One option allows for screening of your baby’s blood type and potentially avoiding a RhoGAM injection if you are Rh negative. There has not been much research examining the role of cell-free DNA testing in single-gene disorders (such as cystic fibrosis), but this may be possible in the near future.
While it may seem that cell-free DNA is the answer for prenatal testing for those parents who want as much information as soon as possible, there are some things to consider first. Most experts recommend that this testing be done only with pregnancies at higher risk for problems, such as those in women of advanced maternal age, at risk for babies with genetic problems, or who have abnormal ultrasound findings in their pregnancy.
Some expectant moms may receive a “failed analysis” result, which indicates that not enough fetal DNA was seen. Therefore, the test is unable to give you information about the pregnancy. This ranges from one to eight percent of all test results. Often, you are able to repeat the blood draw slightly later in your pregnancy, with an analysis sometimes possible at this time.
Most important, while early results are reassuring, cell-free DNA testing is still considered a screening and not a diagnostic test. This means that experts advise that patients with an abnormal test result for a chromosomal abnormality undergo a traditional invasive test to confirm it. Additionally, there is the rare possibility that the test may miss an abnormality. Therefore, if you want to know about your baby’s chromosomes with complete certainty, for now the best route for you to take still may be CVS or amniocentesis.
Logistically, there are several companies that use the new technology, and they are all slightly different in the information they are able to report to you. Most healthcare providers have a company or two with whom they have set up this type of cell-free DNA testing. The blood draw occurs at the end of your first trimester — at approximately nine to ten weeks into your pregnancy — and it takes about one to two weeks to analyze it and report back to you. Women expecting twins are still eligible for this testing but only through a smaller group of companies.
Lastly, some insurance companies pay for a portion of this test, and some may not cover it at all, depending upon your policy. You may have a co-pay of several hundred dollars, especially if your pregnancy is considered low-risk.
Your provider or insurance company should have this information available to you before you decide on a cell-free DNA test. Given the many factors that may influence a decision to have any kind of prenatal genetic testing, it is always best to talk to your provider about which option is best for you.
Mimi Wachendorf Fradinho, MD, is chief resident in the Department of Obstetrics and Gynecology, Beth Israel Deaconess Medical Center, Boston, MA.