What is a karyotype test?

A karyotype test looks at the size, shape, and number of your chromosomes. Chromosomes are the parts of your cells that contain your genes. Genes are parts of DNA passed down from your mother and father. They carry information that determines your unique traits, such as height and eye color.

People normally have 46 chromosomes, divided into 23 pairs, in each cell. One of each pair of chromosomes comes from your mother, and the other pair comes from your father.

If you have more or fewer chromosomes than 46, or if there is anything unusual about the size or shape of your chromosomes, it can mean you have a genetic disease. A karyotype test is often used to help find genetic defects in a developing baby.

Other names: genetic testing, chromosome testing, chromosome studies, cytogenetic analysis

What is it used for?

A karyotype test may be used to:

• Check an unborn baby for genetic disorders
• Diagnose a genetic disease in a baby or young child
• Find out if a chromosomal defect is preventing a woman from getting pregnant or is causing miscarriages
• Check a stillborn baby (a baby that died late in pregnancy or during birth) to see if a chromosomal defect was the cause of death
• See if you have a genetic disorder that could be passed along to your children
• Diagnose or make a treatment plan for certain types of cancer and blood disorders

Why do I need a karyotype test?

If you are pregnant, you may want to get a karyotype test for your unborn baby if you have certain risk factors. These include:

• Your age. The overall risk of genetic birth defects is small, but the risk is higher for women who have babies at age 35 or older.
• Family history. Your risk is increased if you, your partner, and/or another one of your children have a genetic disorder.

Your baby or young child may need a test if he or she has signs of a genetic disorder. There are many types of genetic disorders, each with different symptoms. You and your health care provider can talk about whether testing is recommended.

If you are a woman, you may need a karyotype test if you've had trouble getting pregnant or have had several miscarriages. While one miscarriage is not uncommon, if you have had several, it may be due to a chromosomal problem.

You may also need a karyotype test if you have symptoms of or have been diagnosed with leukemia, lymphoma, or myeloma, or a certain type of anemia. These disorders can cause chromosomal changes. Finding these changes can help your provider diagnose, monitor, and/or treat the disease.

What happens during a karyotype test?

For a karyotype test, your provider will need to take a sample of your cells. The most common ways to get a sample include:

• A blood test. For this test, a health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.
• Prenatal testing with amniocentesis or chorionic villus sampling (CVS). Chorionic villi are tiny growths found in the placenta.

For amniocentesis:

• You'll lie on your back on an exam table.
• Your provider will move an ultrasound device over your abdomen. Ultrasound uses sound waves to check the position of your uterus, placenta, and baby.
• Your provider will insert a thin needle into your abdomen and withdraw a small amount of amniotic fluid.
• Amniocentesis is usually done between week 15 and 20 of pregnancy.

For CVS:

• You'll lie on your back on an exam table.
• Your provider will move an ultrasound device over your abdomen to check the position of your uterus, placenta, and baby.
• Your provider will collect cells from the placenta in one of two ways: either through your cervix with a thin tube called a catheter, or with a thin needle through your abdomen.
• CVS is usually done between week 10 and 13 of pregnancy.

Bone Marrow Aspiration and Biopsy. If you are being tested for or treated for a certain type of cancer or blood disorder, your provider may need to take a sample of your bone marrow. For this test:

• You'll lie on your side or your stomach, depending on which bone will be used for testing. Most bone marrow tests are taken from the hip bone.
• The site will be cleaned with an antiseptic.
• You will get an injection of a numbing solution.
• Once the area is numb, the health care provider will take the sample.
• For a bone marrow aspiration, which is usually performed first, the health care provider will insert a needle through the bone and pull out bone marrow fluid and cells. You may feel a sharp but brief pain when the needle is inserted.
• For a bone marrow biopsy, the health care provider will use a special tool that twists into the bone to take out a sample of bone marrow tissue. You may feel some pressure on the site while the sample is being taken.

Will I need to do anything to prepare for the test?

You don't need any special preparation for karyotype testing.

Are there any risks to the test?

There is very little risk to having a blood test. You may have slight pain or bruise at the spot where the needle was put in, but most symptoms go away quickly.

Amniocentesis and CVS tests are usually very safe procedures, but they do have a slight risk of causing a miscarriage. Talk to your health care provider about the risks and benefits of these tests.

After a bone marrow aspiration and biopsy test, you may feel stiff or sore at the injection site. This usually goes away in a few days. Your health care provider may recommend or prescribe a pain reliever to help.