karyotype test

test overview

karyotype is a test to identify and evaluate the size, shape, and number of chromosomes in a sample of body cells. extra or missing chromosomes, or abnormal positions of chromosome pieces, can cause problems with a person's growth, development, and body functions.

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 a woman from becoming pregnant 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 counsellor. this type of counsellor 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 counsellor can help you make well-informed decisions. ask to have genetic counselling 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.