What it is (overview)

Karyotyping is a laboratory test that looks at a person’s chromosomes—the packages of DNA found in nearly every cell. Chromosomes carry genes that influence growth, development, and many body functions. In a karyotype test, a sample of cells (often from blood, bone marrow, or prenatal samples) is processed in the lab so the chromosomes can be photographed and arranged in order by size and shape. This organized picture is called a karyotype.

The test checks for:

1) Chromosome number problems (aneuploidy): This means there are too many or too few chromosomes. For example, an extra chromosome 21 causes Down syndrome.

2) Chromosome structure problems (structural abnormalities): This includes missing pieces (deletions), extra pieces (duplications), swapped pieces (translocations), or flipped segments (inversions). Some structural changes are inherited (hereditary conditions), while others can happen in specific tissues such as cancer cells.

What results can mean (in plain language):

A normal karyotype usually means the chromosomes in the tested cells look typical in number and structure (for example, 46,XX or 46,XY). An abnormal karyotype means a chromosome difference was found. Depending on the finding, it may explain symptoms or a health condition (such as a genetic disorder), help guide pregnancy or fertility decisions, or provide critical information for cancer diagnosis and treatment planning. Some changes are harmless “variants,” so results are often reviewed with a specialist and may be paired with genetic counseling or additional genetic testing.

When & why it's usually done

Doctors order karyotyping when they suspect a chromosome-related condition or when chromosome information could change medical care. Common reasons include:

Pregnancy and prenatal testing: Karyotyping may be used during prenatal testing (such as after chorionic villus sampling or amniocentesis) if screening tests suggest a higher chance of aneuploidy or if ultrasound shows certain birth differences. It can help diagnose chromosome conditions before birth.

Fertility and reproductive health: Karyotyping may be recommended for individuals or couples with infertility, repeated miscarriages, stillbirth history, or difficulty conceiving. Certain balanced chromosome rearrangements (like balanced translocations) may not cause symptoms in a parent but can increase the risk of pregnancy loss or chromosome conditions in a child.

Newborns, children, or adults with developmental concerns: It may be ordered when there are signs of a possible genetic disorder, such as developmental delay, intellectual disability, growth differences, congenital anomalies (birth defects), differences in sexual development, or delayed/absent puberty.

Evaluation of blood disorders and cancers: In many leukemias, lymphomas, and some other cancers, tumor cells can have characteristic chromosome changes. Karyotyping helps with cancer diagnosis, risk stratification (prognosis), and treatment decisions, and it may be used to monitor response or relapse in certain settings.

Family history and genetic counseling: If there is a known chromosome rearrangement in the family, or a history of hereditary conditions, a clinician may recommend karyotyping as part of genetic counseling and risk assessment.

Common diseases related to it

• Down syndrome (Trisomy 21)
• Edwards syndrome (Trisomy 18)
• Patau syndrome (Trisomy 13)
• Turner syndrome (45,X)
• Klinefelter syndrome (47,XXY and related sex chromosome aneuploidy)
• Structural chromosomal abnormalities (e.g., balanced translocation, Robertsonian translocation, deletion, duplication, inversion)
• Recurrent pregnancy loss related to parental chromosomal rearrangements
• Infertility associated with chromosome number or structure differences
• Chronic myeloid leukemia (Philadelphia chromosome, t(9;22))
• Acute leukemia or myelodysplastic syndromes with characteristic chromosomal changes

Health goals where it may help

• Identifying the cause of suspected genetic disorders by evaluating chromosomes
• Clarifying reproductive risks and supporting fertility planning (including evaluation after recurrent miscarriage)
• Supporting informed decision-making in prenatal testing and pregnancy care
• Guiding genetic counseling for individuals and families with hereditary conditions or known chromosome rearrangements
• Improving cancer diagnosis and treatment planning by detecting tumor-related chromosome changes
• Helping assess prognosis and, in some cases, monitoring response in hematologic cancers (blood cancers)