NIPT, which analyzes cell-free fetal DNA circulating in maternal blood, is a new option in the prenatal screening and testing paradigm for trisomy 21 and a few other fetal chromosomal aneuploidies.
NIPT Test Characteristics
Genetic testing using cell-free fetal DNA
DNA from the fetus circulates in maternal blood. Unlike intact fetal cells in maternal blood, which can persist for years after a pregnancy, circulating cell-free fetal DNA (ccffDNA) results from the breakdown of fetal cells (mostly placental) and clears from the maternal system within hours. Fetal DNA detected during a pregnancy, therefore, represents DNA from the current fetus. Although only about 10-15% of the cell-free DNA circulating in maternal blood is from the fetus, it can be detected and measured. Quantitative differences in chromosome fragments in maternal blood can be used to distinguish fetuses affected with trisomy 21, and a few other fetal aneuplodies, from those that are not affected.
When NIPT is performed
Testing can be done any time after 10+ weeks; typically it is done between 10-22 weeks. Results can take a week or more.
Maternal indications for NIPT
NIPT technologies have been validated in singleton pregnancies at high risk for trisomy 21 due to:
- advanced maternal age
- an abnormal serum screen
- personal or family history of aneuploidy
- abnormal ultrasound
At least one laboratory will accept samples that do not meet these high risk criteria. Additionally, at least one laboratory offers the test in twin pregnancies, and another for Turner syndrome (monosomy X) when the fetus presents with a cystic hygroma. Contact individual laboratories for additional information.
There are several companies that offer the less invasive NIPT testing including MaterniT21™ PLUS, Harmony, Verify and Panorama.
Speak to your physician to discuss the best option for you.
The testing is non-invasive, involving a maternal blood draw, so the pregnancy is not put at risk for miscarriage or other adverse outcomes associated with invasive testing procedures. There is the risk of possibly missing the diagnosis.
Excerpt from NCHPEG, National Coalition For Health Professional Education in Genetics, PDF Factsheets, Table and Web pages modified on 08-15-2012