Until recently, the techniques available to definitively diagnose potential abnormalities and birth defects prenatally were both invasive and risky. Amniocentesis and chorionic villus sampling, however informative, are associated with an increased risk of miscarriage. Medical professionals have been researching new ways to give pregnant women the diagnostic information they want without putting their fetus at risk. A revolutionary screening method known as cell-free fetal DNA (cffDNA) testing is becoming a viable solution to this problem.
The cffDNA test is quite simple. All an expectant mother has to do is give a sample of blood and wait a period of two weeks for the results. The test can be given as early as 10 weeks into the pregnancy. The lab takes the maternal blood sample and measures the fetal DNA inside to determine the odds of the fetus having Down syndrome, Edward syndrome, and Patau syndrome. In order to do this, relative amounts of DNA from chromosomes 21, 18, and 13 (all associated with the above syndromes, respectively) are individually calculated from the blood sample.
The cffDNA test is allegedly very accurate, with over a 99% accuracy rate for predicting Down syndrome, over a 98% accuracy rate for predicting trisomy 18, and approximately a 65% accuracy rate for predicting trisomy 13. However, these rates are only valid for women that are considered “high-risk” for having a pregnancy that results in a genetic abnormality and are not necessarily proven to be as accurate for women that are considered to be at lower risks.
Despite its limitations, cffDNA is a true advance in prenatal testing that may lead to a significant reduction in the need for invasive diagnostic tests that risk the survival of the fetus. Click the link to read the full report regarding advances in prenatal testing from RCOG.