Karyotype genetic testing
A karyotype test is a genetic test that analyzes the chromosomes.
This test uses blood or amniotic fluid, molecular technologies are used to separate the chromosomes, count them, and morphologically analyze them.
The test results can provide information on the presence of chromosomal abnormalities of different kinds, translocations (when pieces of a certain chromosome attach to another chromosome), and other abnormalities.
The test is performed in cases of a risk of chromosome abnormalities, and also in cases of recurring miscarriages, infertility and for evaluating the prognosis in malignant diseases.
When is the test needed?
Karyotype testing is one of the basic tests in the field of genetics, it is recommended in all cases of a risk for chromosomal abnormalities. The test helps detect chromosomal defects and provides basic important information on common genetic disorders.
The test is performed in almost all cases of a risk of chromosome abnormalities, such as:
Sonographic abnormalities – when an ultrasound test (such as an anatomy scan or anomaly scan) shows possible signs of a problem in the fetus’ development, karyotype testing is used to look for chromosomal abnormalities. Since these abnormalities result in developmental defects, it is recommended to undergo a keryotype test and amniocentesis when an anatomy scan detects developmental abnormalities.
Irregular screening test results – all pregnant women undergo several screening tests, such as nuchal translucency tests or alpha-fetoprotein tests, to detect chromosomal abnormalities. Irregular results in these tests require undergoing an amniocentesis and karyotype test to check for chromosomal anomalies.
Maternal age – a woman’s age has an impact on the risk for chromosomal abnormalities. The older the mother, the higher the risk for chromosome abnormalities. Foe this reason, it is recommended that women over the age of 35 undergo karyotype and amniocentesis tests.
Family history and balanced translocations – families with a history of chromosomal abnormalities are at higher risk of these defects in pregnancies. If one of the parents has a family history of such a condition, doctors will recommend undergoing a karyotype test in the early stages of the pregnancy, usually after a Chorionic Villus Sampling (weeks 11 – 13).
In addition, in some cases one of the parents may suffer from a balanced translocation. This is a condition where part of a chromosome has reattached to another chromosome. In most cases, this condition does not cause any clinical abnormalities. In these cases, there is a risk of the fetus suffering from an unbalanced translocation, and it is recommended to undergo a karyotype test as early as possible into the pregnancy.
Moreover, parents of children with a chromosome abnormality are at risk of chromosomal abnormalities and should undergo a karyotype test during the pregnancy.
After a miscarriage – in many cases, miscarriages are a result of chromosome abnormalities that prevent the healthy development of the fetus. In some cases, after a miscarriage ending in a D&C (dilation and curettage), the contents of the uterus are sent to be tested for chromosomal abnormalities.
Recurrent miscarriages- Women who experience recurrent miscarriages go through a series of tests including karyotype tests. The karyotype testing is performed on both parents. Since chromosomal abnormalities are the most common cause of miscarriages, a balanced chromosome abnormality in one of the parents can be the cause of the recurring miscarriages, and it is important to diagnose.
Infertility – as part of the evaluation for couples with infertility, a karyotype test is performed to identify chromosome abnormalities that may be the reason for infertility.
How does the test work?
A karyotype test can use a sample of any tissue or body fluid containing DNA. It is usually performed in the following ways:
- Amniocentesis – in amniocentesis, a small amount of amniotic fluid is drawn from the womb during pregnancy. A needle is inserted into the uterus and a small amount of amniotic fluid is withdrawn. Amniocentesis can be performed from week 16 of pregnancy and is considered a safe and simple procedure.
- CVS (chorionic villus sampling) – In this test, a sample of cells is drawn from the placenta. The test usually takes place in weeks 10-13 of the pregnancy, the early stage it can be performed is one of this test’s biggest advantages. It is most suitable for those in high risk for chromosomal defects.
- Blood test and biopsies – these tests are performed on the parents (and not the fetus). It usually consists of a simple blood test. In addition, karyotype testing can also be done using biopsies from tissues, in these cases the test is undergone to estimate prognosis of tumors and diagnose certain types of cancer.
