FREE FETAL DNA DIAGNOSTICS
The test involves drawing and assessing of a blood sample from a pregnant woman ans well as its special molecular analysis. The “fetal DNA” (free, cell-free DNA of fetal origin, or more precisely, of chorion origin) is examined, small amounts of which pass into the mother’s bloodstream. The determination can be performed after week 10 of pregnancy.
The test can be performed in single and twin pregnancies.
FETAL DNA tests detect over 99% of cases of trisomy 21, trisomy 13 and trisomy 18 of a pair of chromosomes. Currently, they enable the assessment of the risk of other trisomies as well as determine the sex of the foetus and the number of sex chromosomes. An extended test version may detect some deletion and duplication syndromes.
In the events of specific indications, other genetic disorders can also be assessed.
The test can be carried out routinely on any willing pregnant woman but, in accordance with current medical knowledge and the applicable recommendations, it should be proposed: when the result of risk calculation based on ultrasound and biochemical double test in the 1st trimester is between 1:100 and 1:1000. This test can also be performed:
– before performing an invasive test if the pregnant woman hesitates to make the final decision.
– if the ultrasound scan results indicate specific abnormalities in the foetus structure with a correct screening test result. In such a situation a prior genetic consultation is necessary aiming at test orientation.
If the risk calculated in the first trimester screening tests is > 1:100, a diagnostic test should be proposed – invasive test.
Currently, fetal DNA screening test has some limitations and is not recommended in multifetal pregnancies of a higher order than twin ones.
THE TEST RESULTS AWAITING TIME is 8-10 days.
Prior to the screening test based on the evaluation of free fetal DNA in the mother’s blood, it is necessary to perform an ultrasound scan aimed at assessing the number of foetuses and gestational age.
WHEN DECIDING ON THE FETAL DNA TEST, IT SHOULD BE REMEMBERED THAT GENETIC SCREENING TEST PERFORMED ON FREE FETAL DNA DOES NOT REPLACE ULTRASOUND SCANS OF THE 1ST and 2ND TRIMESTER.
IN THE CASE OF MOST PATIENTS WITH A DIAGNOSED DEFECT IN THE FOETUSTHERE ARE NO GENETIC DISORDERS*
* possible to be confirmed with the methods available in the world.
Simplified explanatory information for patients concerning the genetic aspect of testing fetal DNA in mother’s blood from the point of view of a genetic specialist is available HERE.
Norton, M., Brar, H., Weiss, J., Karimi, A., et al. Non-Invasive Chromosomal Evaluation (NICE) Study: Results of a Multicenter, Prospective, Cohort Study for Detection of Fetal Trisomy 21 and Trisomy 18, Am J Obstet Gynecol.(2012), Aug;207(2):137.e1-8.
Nicolaides KH, Syngelaki A, Ashoor G, et al. Noninvasive prenatal testing for fetal trisomies in a routinely screened first-trimester population.Am J Obstet Gynecol.(2012), 207:374.e1-6.
Ashoor G, Syngelaki A, Nicolaides KH, et al. Trisomy 13 detection in the first trimester of pregnancy using a chromosome-selective cell-free DNA analysis method, ULTRASOUND Obstet Gynecol.(2013), Jan;41(1):21-5.
Gil MD, Quezada MS, Bregant B, Syngelaki A, Nicolaides KH. Cell-free DNA analysis for trisomy risk assessment in first-trimester twin pregnancies. Fetal Diagn Ther.(2013), Nov 15.
Vora NL, Robinson S, Hardisty EE, Stamilio DM. The utility of a prerequisite ultrasound at 10-14 weeks in cellfree DNA fetal aneuploidy screening. Ultrasound Obstet Gynecol. 2016 Jun 14. doi: 10.1002/uog.15995