Non-invasive prenatal tests have been developed in recent years and since 2013 they are offered to pregnant women around the world. In these tests fetal DNA is isolated from a blood sample of a pregnant woman. The sample of fetal DNA is then analysed in order to detect the most common types of fetal chromosomal disorders (Down’s syndrome, trisomy 18 and 13 and defects linked to the sex chromosomes X and Y).
In the Czech Republic three of these tests are currently offered:
- PANORAMA (laboratory Natera, USA, www.natera.com)
- Harmony (laboratory Ariosa, USA, www.harmony-test.cz)
- Prenascan (BGI, China , www.prenascan.eu)
- MaterniT21Plus (Sequenom, USA, www.maternit21.cz)
In our PROFEMA centre blood samples are taken from 10th week of pregnancy for Harmony blood test, and also for MaterniT21Plus test. A blood sample is sent the same day to laboratories in the U.S. Results are available within 14 days.
Additionally, we can forward the patient to the collaborating GENNET laboratory, where the sample is collected for non-invasive prenatal test PRENASCAN. Analysis of samples is carried out in a laboratory in China, results are available within 14 days.
Although non-invasive diagnostic tests were developed as a safe alternative to amniocentesis and other invasive procedures (amniocentesis, CVS, cordocentesis) they cannot fully replace invasive procedures for the following reasons:
- they detect only the most common types of fetal chromosomal defects (invasive procedure can eliminate all types of chromosomal defects)
- In case of positive results, it is necessary to perform invasive procedures and confirm the defect (seldom it may occur that the fetus is not affected by the chromosomal defect )
- In case of a negative result, there is still (though very small) probability that the fetus is affected by the most common chromosomal defect. This can be the case especially after abnormal findings on ultrasound examination of the fetus or if a too small sample of DNA is obtained from the mother’s blood (expressed as so called fetal fraction in Harmony and MaterniT21Plus tests, unfortunately for Prenascan test this data is missing).
Performance of non-invasive diagnostic test (for the above reasons) is suitable substitute for invasive procedures especially in pregnancies at increased risk of Down´s syndrome ( or trisomy 18 or 13 or abnormalities of sex chromosomes) due to abnormal results of biochemical screening of maternal blood (triple test – HCG , AFP, estriol , PAPP-A , free beta- hCG) , risk that rises from family anamnesis (the incidence of Down´s syndrome in first-degree relatives or in a previous pregnancy) or due to advanced maternal age.
It is also suitable for pregnant women who want the most accurate examination of the fetus for most common types of chromosomal defects (primarily Down´s syndrome ) and do not want to take risks associated with amniocentesis or other invasive procedures (0.5 % increased risk of miscarriage). If results of detailed ultrasound examination performed by an experienced doctor and outcome of non-invasive diagnostic test are negative, the risk of having a fetus with Down´s syndrome and other chromosomal defects is very unlikely.