Why It Is Done

Karyotyping is done to:

• Find out whether the chromosomes of an adult have a change that can be passed on to a child.
• Find out whether a chromosome defect is preventing pregnancy or is causing miscarriages.
• Find out whether a chromosome defect is present in a fetus. Karyotyping also may be done to find out whether chromosomal problems may have caused a fetus to be stillborn.
• Find out the cause of a baby's birth defects or disability.
• Help determine the appropriate treatment for some types of cancer.
• Identify the sex of a person by checking for the presence of the Y chromosome. This may be done when a newborn's sex is not clear.

How To Prepare

You do not need to do anything before you have this test.

Since the information obtained from karyotyping can have a profound impact on your life, you may want to see a doctor who specializes in genetics (geneticist) or a genetic counselor. This type of counselor is trained to help you understand what karyotype test results mean for you, such as your risk for having a child with an inherited (genetic) condition like Down syndrome. A genetic counselor can help you make well-informed decisions. Ask to have genetic counseling before making a decision about a karyotype test.

How It Is Done

Karyotype testing can be done using almost any cell or tissue from the body. A karyotype test usually is done on a blood sample taken from a vein. For testing during pregnancy, it may also be done on a sample of amniotic fluid or the placenta.

Blood sample from a vein

A health professional uses a needle to take a blood sample, usually from an arm.

Cell sample from a fetus

For this type of test, cells are collected from the fetus using amniocentesis or chorionic villus sampling.

Cell sample from bone marrow

Bone marrow aspiration may be used for a karyotype test.

Watch

How It Feels

Karyotype testing is usually done using a blood sample from a vein. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.

Risks

Blood sample from a vein

There is very little chance of having a problem from this test. A small bruise may form at the site.

Results

Karyotype is a test to identify and evaluate the size, shape, and number of chromosomes in a sample of body cells.

Results of a karyotype test are usually available within 1 to 2 weeks.

Normal:

• There are 46 chromosomes that can be grouped as 22 matching pairs and 1 pair of sex chromosomes (XX for a female and XY for a male).
• The size, shape, and structure are normal for each chromosome.

Abnormal:

• There are more than or fewer than 46 chromosomes.
• The shape or size of one or more chromosomes is abnormal.
• A chromosome pair may be broken or incorrectly separated.