A screening test called the cell free fetal DNA test is available for all women. A small amount of fetal DNA circulates in the mother’s blood. This DNA mainly comes from the placenta. The cell free fetal DNA in a sample of the mother’s blood can be screened for Down syndrome, trisomy 13, trisomy 18, and sex chromosome abnormalities. In women who are at high risk of having a baby with a chromosome disorder, this test is 99% accurate in detecting cases of Down syndrome and has a low rate of false-positive results. This test can be done as early as 10 weeks of pregnancy in some women. Results take about 1 week to process.
At this time, the cell free fetal DNA test is recommended only for women who have an increased risk of having a child with a chromosome disorder, such those older than 35 years and those with an abnormal ultrasound, abnormal first or second trimester screen result, or women who already have a child with a chromosome disorder. It is not recommended for women at low risk of having a baby with a chromosome disorder or women carrying more than one baby because it has not been tested sufficiently in these groups.
The cell free fetal DNA test has certain limitations. It does not screen for neural tube defects. An additional screening test needs to be done to check for these disorders, however, neural tube defects may also be detected on ultrasound. In addition, although it is highly accurate in detecting chromosome problems in high-risk women, it is not as accurate as diagnostic tests. If you have a positive cell free fetal DNA test result, diagnostic testing (amniocentesis) is recommended.
The above genetic screening tests will not tell you “yes” or “no” if your baby has a chromosomal condition such as Down Syndrome; instead it will tell you if there is a high or low possibility of your baby having the condition.
An important issue to consider is how much this test will cost. Cell free fetal DNA testing is not considered standard of care and some insurance companies consider this test “experimental.” It is important to check with your insurance if you have concerns about the cost of this screening test.