A karyotype test is a type of genetic testing. It looks at the size, shape, and number of chromosomes in a sample of cells from your body. Chromosomes are found in the cell nucleus, which is like the command center of a cell. Chromosomes contain your genes. Genes carry information, called DNA, that controls what you look like and how your body works.
You inherit your chromosomes from your parents. Normally, all your cells (except for egg and sperm cells) have a set of the same 46 chromosomes. The chromosomes are grouped into 23 pairs. Each pair has two chromosomes, one coming from each parent. You may develop certain genetic disorders if your cells:
- Are missing whole chromosomes or pieces of chromosomes
- Have extra chromosomes or extra pieces of chromosomes
A karyotype test checks the chromosomes in your cells to:
- See whether you have a full set of 46 chromosomes. Having too many or too few chromosomes can cause serious problems with health, growth, and normal development, such as Down syndrome (extra chromosome 21) and Turner syndrome (missing X chromosome).
- Look for changes in the structure of chromosomes, such as broken, missing, or extra parts. These changes may cause a wide variety of problems depending on which chromosome is affected. But some changes in chromosomes don’t cause problems.
Certain chromosome problems are present from birth. Chromosome problems can also develop in certain cells after birth. These problems can cause specific types of cancer.
Other names: genetic testing, chromosome testing, chromosome studies, cytogenetic analysis
What is it used for?
A karyotype test looks for unusual changes in chromosomes. It may be used to:
- Check you and/or your family members for specific chromosome problems if you:
- Have a genetic disorder that runs in your family
- Have symptoms that may be from a genetic disorder
- Male or female infertility
- Miscarriages, if you have lost two or more pregnancies before 20 weeks
Why do I need a karyotype test?
You may need a karyotype test if:
- You’re planning to have children or are pregnant:
- To learn whether you and/or your partner have abnormal chromosomes that you could pass on to a baby
- To find out why you’re having problems getting pregnant or having miscarriages
- To check your unborn baby for genetic disorders, especially if the baby has a high risk for problems. The risk may be high if:
- The pregnant parent is age 35 or older. The overall risk of genetic birth defects is small, but the risk increases after age 35.
- Either parent has a genetic disorder, a family history of a genetic disorder, or another child with a genetic disorder.
- The results of certain prenatal screening tests weren’t normal.
- Multiple myeloma
What happens during a karyotype test?
For a karyotype test, the type of sample you provide depends on the reason for the test.
To test the chromosomes of an unborn baby, the sample may be gathered using:
- Amniocentesis. This procedure collects a sample of the amniotic fluid that surrounds the unborn baby during pregnancy. The fluid contains cells from the baby that can be tested. Amniocentesis is usually done between week 15 and 20 of pregnancy.
- Chorionic villus sampling (CVS). This procedure collects tissue from the chorionic villi, which are parts of the placenta that usually have the same chromosomes as the unborn baby. (The placenta is the organ that grows in the uterus to provide nutrients and oxygen to the baby.) A CVS is usually done between week 10 and 13 of pregnancy.
To test the chromosomes of adults, children, and babies, the sample may be from:
- A blood test. This is the most common sample used for karyotype tests. A health care professional will use a small needle to remove a blood sample from a vein in your arm.
- A buccal (cheek) swab. A health care professional will insert a swab into your mouth and rub it across the inside of your cheek to gather a sample of cells.
- A bone marrow test. This test may be used if you have a certain type of cancer or blood disorder. Marrow is soft, spongy tissue found inside of bones. Most bone marrow samples are taken from the back of the hip bone.
Will I need to do anything to prepare for the test?
For a CVS or amniocentesis, you may need to drink extra fluid and not urinate before your test so that your bladder is full.
A blood test or cheek swab usually don’t require any preparation.
If you’re having a bone marrow test, ask your provider for instructions about how to prepare.
Are there any risks to the test?
During amniocentesis or CVS, you may feel mild stinging or cramping. Both procedures are safe, but they do have a slight risk of causing miscarriage. Talk with your provider about the risks and benefits of these tests.
A blood test has very little risk. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.
A cheek swab has no risk.
After a bone marrow test, you may feel stiff or sore where the sample was taken. This usually goes away in a few days. Serious risks are rare.
What do the results mean?
A normal or negative result means that there were 46 chromosomes in the sample without any unusual changes in their structure.
An abnormal or positive result means that unusual changes in the number or structure of chromosomes were found. Abnormal results can mean many things about your health or your child’s health depending on the chromosome changes that were found. Talk with your provider to learn what your results mean.
Is there anything else I need to know about a karyotype test?
If you’re thinking about having a karyotype test or have received abnormal results, it may help to talk with a genetic counselor. Genetic counselors can give you information about how genetic conditions might affect you or your family. They can help you find support services and make informed decisions about treatment or management options for a genetic disorder.
Courtesy of MedlinePlus from the National Library of Medicine.