Karyotyping is a test to examine chromosomes in a sample of cells, which can help identify genetic problems as the cause of a disorder or disease. This test can:

• Count the number of chromosomes
• Look for structural changes in chromosomes

The test can be performed on a sample of blood, bone marrow, amniotic fluid, or tissue from the placenta, the organ that develops during pregnancy to feed a growing baby.

To test amniotic fluid, an amniocentesis is done.

A bone marrow specimen requires a bone marrow biopsy.

The sample is placed into a special dish and allowed to grow in the laboratory. Cells are later taken from the growing sample and stained. The laboratory specialist uses a microscope to examine the size, shape, and number of chromosomes in the cell sample. The stained sample is photographed to provide a karyotype, which shows the arrangement of the chromosomes.

Certain abnormalities can be identified through the number or arrangement of the chromosomes. Chromosomes contain thousands of genes that are stored in DNA, the basic genetic material.

There is no special preparation needed.

How the test will feel depends on whether the sample procedure is venipuncture (having blood drawn), amniocentesis, or bone marrow biopsy.