What is this new “fetal DNA” test?
Through the use of genetic sequencing technology on the “cell free DNA” within the mother’s blood, we are now able to detect early in pregnancy almost all cases of Down Syndrome (Trisomy 21) and most cases of Trisomy 18 and 13, two other very serious chromosomal abnormalities in the fetus. This test is being called “Non-Invasive Prenatal Testing”, or NIPT for short. There are a number of different brand names this test is being marketed under, as there are a number of competing companies offering this test.
How does a fetal DNA test work?
We have known for many years that fetuses shed cells into their mom’s circulation during pregnancy, and a great deal of research aimed at analyzing the DNA in these cells has been performed. However obtaining results from fetal cells has proven to be extremely difficult and not practical. Scientists have recently realized that it is actually easier to analyze fetal DNA from cells that have broken down, with the DNA floating free in the maternal serum. This “cell free DNA” forms the basis for an exciting new group of tests.
How good is the test?
NIPT will detect well over 99% of fetuses with Trisomy 21 (Down syndrome), and close to this percentage of Trisomy 18 and 13.
Is the test ever incorrect?
Yes, false positives are possible but not common. We always confirm any abnormal results with additional testing, either a CVS or amniocentesis.
When is the test done?
The test cannot be done before 10 menstrual weeks (eight weeks from conception) as there is not enough fetal DNA present. Generally we order the test in the 10 to 14 week range, although it can be done any time after 10 weeks. An ultrasound is done to verify fetal viability, gestational age, number of fetuses, and the thickness of a small layer of fluid behind the fetal neck, a “nuchal translucency” or “NT”. A thick NT can be a warning sign of additional problems with the fetus. Then blood is drawn, and the results are usually available in 7-10 days.
Does the test tell us the fetal gender?
Yes, the test can determine gender if you desire this information, however the test is not recommended solely for this reason.
Who should get the test?
At the current time, the test is recommended only for patients who are at high risk for chromosome problems. High risk includes maternal age 35 or older, history of a prior chromosomally abnormal pregnancy, or suspicion of chromosomal abnormality on other screening tests or ultrasound.
Why isn’t it recommended for low risk patients?
The test has been tested extensively in high risk populations where Down Syndrome is more common. Any time the frequency of a problem is lower, it reduces the accuracy of a given test. Therefore in a low risk population, there is a higher chance that the test would not detect a problem, and a higher chance of a false positive. However early testing in low risk populations appears to be favorable, and likely the test will be released for low risk populations in the future.
Does this test replace an amniocentesis or CVS?
Amniocentesis or CVS gives us a picture of all chromosomes, and allows a detailed view of each chromosome. NIPT, at this time, only gives us a numerical count of the number of the number 21,18 and 13 chromosomes, plus the X and Y. On the other hand, amniocentesis and CVS are procedures, that while very safe, do carry a very small risk of causing a pregnancy loss. So amnio/CVS are better, but more risky. In most “routine” cases, we are performing NIPT, using amnio/CVS only when a positive result is obtained on NIPT in order to confirm the abnormal result. However in certain very high risk cases, amnio/CVS may be considered from the start, bypassing NIPT.
How much does the test cost and will my insurance pay for it?
The “list price” for the test varies between different companies, but can be from $800 to several thousand dollars. Most of the companies performing the test will have a “cash pay” discount available, usually less than $300. Most, but not all, insurance companies will pay for the test IF you are in the high risk category. Be aware that many times the cost of the test may hit your deductible. If you do not fall in the high risk category, and are considered low risk, very few if any insurance companies will pay for the test at this time. As with all tests and procedures, we cannot guarantee what your insurance will cover.