Non-invasive Prenatal Screening with Cell-free DNA
What is Non-invasive Prenatal Screening with Cell-free DNA?
Non-invasive prenatal testing or screening (NIPT) by evaluation of cell free fetal DNA is a recently developed maternal blood test to detect common fetal trisomies (trisomy 21—Down syndrome, trisomy 18 and Trisomy 13) during the first and second trimesters.
In contrast to invasive diagnostic testing (CVS and amniocentesis), NIPT does not pose a risk of miscarraiage to the pregnancy since it involves only a maternal blood sample. There are multiple laboratories now offering this testing with their own trademark names.
What is a trisomy?
Humans have 23 pairs of chromosomes, which are strands of DNA and proteins that carry genetic information. A trisomy is a chromosomal condition that occurs when there are three copies of a particular chromosome instead of the expected two.
Trisomy 21 is due to an extra copy of chromosome 21 and is the most common trisomy at the time of birth. Trisomy 21 causes Down syndrome, which is associated with mild to moderate intellectual disabilities and may also lead to digestive issues and congenital heart defects. It is estimated that Down syndrome is present in one out of every 740 newborns.
Trisomy 18 is due to an extra copy of chromosome 18. Trisomy 18 causes Edwards syndrome and is associated with a high rate of miscarriage. Infants born with Edwards syndrome may have various medical conditions and a shortened lifespan. It is estimated that Edwards syndrome is present in approximately one out of every 5,000 newborns.
Besides trisomy 21 and trisomy 18, there are other trisomies which are less common at birth or associated with milder medical conditions.
How is non-invasive prenatal testing (NIPT) by evaluation of fetal cell free DNA different from other prenatal tests?
Other screening tests such as Full Integrated Screening, other serum blood tests and ultrasound are also noninvasive, but can be less sensitive.
Diagnostic tests such as amniocentesis or chorion villus sampling (CVS) are accurate for detecting fetal trisomies , but are invasive and pose a slight risk for fetal loss.
Who can get non-invasive prenatal testing?
Non-invasive prenatal screening can be ordered by healthcare professionals for women with pregnancies of at least 10 weeks gestational age.
What information with non-invasive prenatal testing offer to me and my physician?
Detection rates for Trisomy 21 (Down syndrome) are up to 80-99%. Detection rates for trisomy 18 (Edwards syndrome) are up to 97.2-99.9% and for trisomy 13 (Patau syndrome) are up to 78.6-91.7%.
Low Risk result: With a Low Risk result , the chance of having a baby with Trisomy 21, Trisomy 18, or Trisomy 13 is low. In rare instances, the test will not detect these birth defects as it cannot detect all affected pregnancies.
High Risk result: If testing indicates a High Risk, there is an increased chance of having a baby with Trisomy 21, Trisomy 18, or Trisomy 13. If your result is High Risk, your healthcare provider may offer genetic counseling and/or diagnostic testing to determine if you baby is affected with one of these conditions.
Non-invasive prenatal testing detects cell free DNA fragments from both the mother and fetus in the mother’s blood circulation to determine if there is an increased quantity of a particular chromosome as would be seen in a trisomy pregnancy.