Invasive Prenatal Testing
The term ‘invasive screening’ refers to prenatal screening tests that involve taking a sample of the mother’s amniotic fluid or placenta using a very fine needle. Amniocentesis and chorionic villus sampling are two invasive prenatal methods. There is still a small risk of miscarriage, although the safety rate of invasive methods has increased significantly compared to the past. Based on international literature, chorionic villus sampling is associated with a small miscarriage rate of 0.1-0.2% while amniocentesis with a small miscarriage rate of 0.1%, if performed by a qualified physician. Prenatal genetic testing is done when there is a high chance that a child will be born with a genetic abnormality. The genetic abnormality may include chromosomal abnormalities and/or gene mutations in the fetus.
More specifically, indications for invasive prenatal testing are:
- Maternal age > 35 years
- Abnormal biochemical (PAPP-A) or ultrasound findings (e.g. cervical transparency, congenital anomalies)
- Previous child or/and prior pregnancy with a chromosomal abnormality
- Parent carrier of a balanced chromosomal rearrangement or with a known gene disease mutation
- History of multiple miscarriages, infertility
- Mother carrying a sex-linked disease
- Abnormal findings in non-invasive prenatal testing (NIPT)
- Parental desire due to stress. Anxiety about pregnancy.
A chorionic villus sampling (CVS) is an invasive diagnostic procedure in which a small sample of the placenta is taken, and its cells are examined. The extracted genetic material of the placenta is identical to that of the fetus, so the chromosomes present in its cells can give an insight into the genetic make-up of the fetus. In this way, we can rule out or confirm the presence of a chromosomal or genetic abnormality in the fetus.
Trophoblast is collected after the 11th week of pregnancy, the maximum recommended control week being 15 weeks.
Amniocentesis is an invasive diagnostic test in which the cells of the amniotic fluid are examined. This is an examination of the genetic material of the fetus, in order to detect any chromosomal abnormalities. Amniotic fluid is a clear, yellow liquid found in the amniotic sac that surrounds the developing embryo. Amniotic fluid is made from the urine of the fetus and contains cells from the kidneys, lungs, gastrointestinal tract and skin.
Amniocentesis is performed after the 16th week of pregnancy. Ideally, it should be done between 16 and 22 weeks of pregnancy. The maximum recommended time for the test is 32 weeks.
Chromosomal aneuploidies, more or less frequent, can be detected by molecular analysis. Τhe most common chromosomal aneuploidies, such as Down syndrome (trisomy 21), Pateau syndrome (trisomy 13), Edwards syndrome (trisomy 18), Turner syndrome (monosomy X) and other sex chromosome aneuploidies (XXX, XY, XYY, etc.) can be screened in less than 48 hours with the QFPCR method. Comparative genomic microarray hybridisation (array-CGH) using ~60,000 oligonucleotide probes covering the entire genome while targeting approximately 500 genomic regions known to be associated with genetic syndromes. The karyotype test (with special G-banding staining) is performed by microscopic analysis and gives information about the number and structure of the chromosomes but also for some structural rearrangements. ASTREA HEALTH offers testing for all chromosomal analyses. You can find them in the corresponding list.
In cases where there is a family history of a carrier or sufferer of a genetic disease (e.g. cystic fibrosis, thalassaemia), prenatal screening for mutations is possible by analysing the DNA of the fetus and the parents. ASTREA HEALTH offers testing for all genetic diseases. You can find them in the corresponding list.
Sample type: Chorionic villi and amniotic fluid. We will collect the sample from the doctor taking it or you can bring it to us.
Time to obtain result: 24h-2 weeks. This will depend on the type of exam package that you choose to take.