Noninvasive prenatal testing from cell-free DNA

Abstract

The test analyzes fragments of DNA derived from the placenta circulating in maternal blood. The sensitivity and specificity of noninvasive prenatal testing depend on the chromosome being analyzed and also vary by testing laboratory. For trisomy 21 (Down syndrome), both sensitivity and specificity of the tests tend to be greater than or equal to 99%.1-5 Most studies to date do not provide positive or negative predictive values. Of note, authors of most published studies have commercial affiliations with testing laboratories. Pre- and posttest counselling should include a discussion of the limitations of this testing.3 Most noninvasive testing only addresses aneu ploidies of chromosomes 21, 13 and 18, with optional analysis of the sex chromosomes. No information is pro vided about other genetic conditions, congenital anomalies or other parameters of fetal or maternal health. Test failure can occur when there is insufficient fetal DNA, which can be related to maternal weight, gestational stage, or technical or sampling issues.5 This testing has not been well studied in multiple gestations.3