Non Invasive Prenatal Screening ( N.I.P.S.) or Cell free DNA Testing
By Dr. Stovall
Introduction: Chromosomal testing with gender identification in the first trimester
New to prenatal screening is the N.I.P.S. testing. It is a chromosomal test for Down’s syndrome and other genetic disorders. It is getting a lot of attention not only for increased sensitivity to check for Down’s syndrome, but its ability to find out the baby’s gender in the first trimester. This blog article will go over that testing and when it is appropriate to order.
History of testing for genetic disorders
Amniocentesis was the first testing for genetic conditions such as Down’s syndrome. This was not a popular test as it is invasive and carries a risk of harm to the baby. Now we have many non-invasive options for screening that can give information about the genetics of the baby without the potential harm of an amniocentesis. Amniocentesis is the only chromosomal study to give absolute assurance that the baby does not have a genetic disorder, but the new screening tests are getting better.
Current screening options for genetic disorders
Current tests used to screen for genetic conditions are serum (or blood) tests on the mother with or without an ultrasound. Here are a few of the most popular:
- Quad screening
Blood draw from the mother at about 15-20 weeks of pregnancy. Four proteins, including the alpha fetoprotein that come from the placenta are evaluated by calculating the amount in the mother’s blood.
- 1st Trimester screen
An ultrasound down in the first trimester to look at the back of the baby’s neck and to measure the nuchal translucency. This is combined with a blood test at the time of the ultrasound measuring different proteins and hormones from the placenta.
- Integrated screening
Combines the Quad screen and the first trimester screen.
These tests, except amniocentesis, are considered screening tests. They separate out the high risk pregnancies from the low risk pregnancies. If any of these tests showed that the baby was at increased risk for Down’s syndrome or other genetic disorders, then we would offer to do a targeted ultrasound and amniocentesis to obtain fluid from the sac around the baby to do chromosome studies.
NIPS: the newest genetic screening test
The newest genetic screening is the N.I.P’s or cell free DNA testing. DNA from the placenta that is in the mother’s blood is tested for chromosomal problems. (such as Down’s syndrome, trisomy 18, and sex chromosome problems). Because this is a chromosomal test, it can give results about the gender of the baby. It does not, however, test for all possible genetic disorders. For example, if the mother or the father has an inherited condition like cystic fibrosis, that is tested with a separate genetic test. The advantage to this test is that it is a chromosomal test without the risk of an amniocentesis.
N.I.P’s testing is done when the integrated screening or other genetic testing shows an increased risk for Down’s syndrome. If the NIPS test is negative, then we can be 99% sure the baby does not have Down’s syndrome, but it does not mean that the baby does not have another genetic disorder or syndrome. In this way the NIPS testing decreases the amount of invasive testing (or amniocentesis) done for positive screening.
Problems with the NIPS testing
NIPS sounds great with its ability to find out the gender of the baby in the first trimester and the high sensitivity for Down’s syndrome, but it comes with a down side as well. The first is the cost. It is more expensive than the other screening tests and it is not covered by all insurance carriers without a positive integrated screen or advanced maternal age (age over 35.) The NIPS only screens for about 60% of possible genetic disorders. Also, NIPS testing does not test for birth defects such as spina bifida or anacephaly, both of which are tested with current screening recommendations.
Conclusion
In the near future, as the cost to do DNA testing goes down, we will probably switch to NIPS testing with the first trimester screen as a standard to test for genetic disorders and birth defects. For now, we are recommending using NIPS in high risk patients or patients with a positive integrated screen.
