Understanding Karyotypes and Reasons for Genetic Testing

Medically Reviewed By Avi Varma, MD, MPH, AAHIVS, FAAFP
Was this helpful?
5

Your karyotype is your collection of chromosomes, which carry your genetic information. The term “karyotype” also refers to the process of producing an image of these chromosomes. A typical human cell has 23 pairs of chromosomes, making 46 chromosomes in total. You inherit 23 chromosomes from each parent.

A karyotype allows doctors and other healthcare professionals to view a person’s chromosomes. During pregnancy, doctors and parents may use this test to identify possible genetic disorders. These disorders may occur when there is an extra or missing chromosome on the karyotype. Down syndrome and Turner syndrome are examples of such disorders.

This article will provide an overview of karyotypes, including types of karyotype tests and what results of these tests mean.

What is a karyotype?

Karyotypes are tests that assess your genetic makeup. They can count your chromosomes and analyze their sizes and shapes.

Your chromosomes hold your genes, and your genes dictate your traits. Everything from your skin color to your height is a product of your genes.

Pregnant woman consulting with doctor or genetic counselor
This is an example of a normal human karyotype, which is an individual’s collection of chromosomes. The term ‘karyotype’ also refers to a laboratory technique that produces an image of an individual’s chromosomes. Credit: kanyanat wongsa/Shutterstock

If there is a change or mutation in the chromosomes, a genetic disorder may develop. Changes to the chromosomes occur when:

  • A part of a chromosome duplicates.
  • A part of a chromosome is missing.
  • A part of one chromosome detaches and attaches itself to another chromosome.
  • Two chromosomes exchange material.

A karyotype will investigate if any of these changes have occurred. Karyotypes are also called cytogenetic analysis and genetic testing.

Purpose of karyotype tests 

Doctors may be able to treat a disorder more effectively when they understand its root cause. Karyotypes help doctors better understand the root causes of genetic disorders and chromosomal abnormalities.

Prospective parents can also benefit from karyotypes that identify whether they are carriers of certain gene mutations or chromosomal changes. This information can help them determine the risk of having a child who inherits a genetic disorder.

Conditions commonly diagnosed with karyotype tests

Doctors and parents may use karyotypes during pregnancy to test an unborn child. After delivery, if a child begins to show symptoms, a karyotype can confirm a diagnosis of a genetic disorder.

The most common genetic conditions a karyotype can identify include:

  • Turner syndrome: This occurs when a female has a missing or damaged X chromosome. Possible effects include heart problems, short height, and failure of ovarian development.
  • Down syndrome: This is when a person has one duplicate chromosome 21, for a total of three. It is also known as trisomy 21. This condition affects learning abilities, physical growth, and facial appearance.
  • Edwards syndrome: In this case, a child has an additional chromosome 18. This can result in low birth weight and a short height.
  • Patua syndrome: Also known as trisomy 13, this is the result of a child having three copies of chromosome 13. The condition can cause severe intellectual disability, congenital heart defects, spinal cord problems, and extra fingers or toes.
Print
This is an example of a human karyotype consistent with Down syndrome. Down syndrome is also known as ‘trisomy 21’ because of the extra copy of chromosome 21 that defines this condition. Credit: kanyanat wongsa/Shutterstock

Who needs a karyotype test?

Doctors usually recommend karyotypes to pregnant people who are 35 years and older. This is because research shows that the risk of certain genetic disorders is higher when pregnancy occurs at a later age.

Other factors that may indicate a need for genetic testing include:

  • Recurrent miscarriages: Experiencing two or more miscarriages may indicate the presence of a chromosomal issue in one or both parents.
  • Cancers and blood disorders: If a person has a blood disorder or cancer, such as leukemia or lymphoma, doctors may perform a karyotype to determine the best treatment approach.
  • Family history of disease: A person who has a family history of genetic disorders may need a karyotype to see if they are a carrier for the specific disorder.
  • Unusual ultrasound: In the first trimester, doctors perform a nuchal translucency screening, which looks for the presence of fluid collecting behind the neck of the fetus. This can be an accurate first step in identifying genetic disorders such as Down syndrome, which can be confirmed through a karyotype.
  • Abnormal results from noninvasive prenatal tests: These tests use a blood sample to detect fetal DNA in the pregnant parent’s plasma. High amounts of DNA from either the sex chromosomes (X and Y) or chromosomes 13, 18, and 21 can indicate the presence of associated genetic disorders.

Talk with your doctor about your individual risk factors to determine if you and your partner might benefit from karyotype testing.

What to expect from a karyotype procedure

There are many methods to collect a sample for karyotype testing. Doctors may use each type to look for a different problem. However, they all use samples of your blood or bodily fluids for the test.

Common types of karyotype procedures include:

  • Blood test: For anyone who may want or need a karyotype, doctors can use a blood sample to perform a genetic analysis.
  • Amniocentesis: This test can detect problems with a fetus’s development. Your doctor will examine your abdomen with an ultrasound device. They will also draw a small amount of amniotic fluid from your abdomen with a needle. This test can also reveal the positions of your uterus, placenta, and fetus. Doctors usually perform it about 15–20 weeks into pregnancy.
  • Chorionic villus sampling (CVS): This test is similar to amniocentesis, but uses the cells of the placenta rather than amniotic fluid. Your doctor will examine your abdomen and extract placental cells through your cervix. You may feel mild cramping. Doctors perform CVS about 10–13 weeks into pregnancy.
  • Bone marrow biopsy: This test can diagnose certain cancers and blood disorders. Your doctor will take a sample of your bone marrow, typically from your hip, using a special device that reaches into the bone. Doctors will administer mild sedation, though you may still feel pressure during the procedure.

Amniocentesis and CVS testing each carry a small risk of miscarriage. Talk with your doctor about your individual risk factors and any concerns you may have to determine the right tests for you.

What do the results of a karyotype test mean?

Pregnant woman consulting with doctor or genetic counselor
Raymond Forbes LLC/Stocksy United

If there are structural abnormalities with your chromosomes, you may have a genetic disorder or be a carrier for one. Structural abnormalities include abnormal chromosome shapes or sizes. The presence of additional or missing chromosomes may also indicate a genetic disorder.

The results of a karyotype can have a range of implications depending on the situation. For someone with a leukemia diagnosis, genetic testing can help doctors identify specific traits of the cancer and plan effective treatment.

For prospective parents, learning about a fetus’s genetic disorder can allow them to research information, find resources, review risks to the fetus and birthing parent, or possibly decide to end the pregnancy.

Genetic counseling 

Because the results of a karyotype can have a profound impact on your life, you may want to consult a genetic counselor before or after taking a karyotype test.

A genetic counselor can explain testing procedures in detail and answer any questions you may have. They can also talk you through possible result scenarios and help you prepare.

After the test, a genetic counselor can explain the results to you. They can also refer you to the appropriate specialist to discuss the next steps.

Summary

Karyotypes are lab tests that provide information about your genetic makeup. They can count your chromosomes as well as examine their sizes and shapes.

Typically, a person has 46 chromosomes. If there is a missing or extra chromosome, this indicates a genetic disorder. Such disorders include Down syndrome and Edwards syndrome.

Doctors often recommend karyotypes to pregnant people above 35 years of age. People with cancers or blood disorders may also take the test as part of their diagnosis to help inform treatment plans.

Types of karyotype procedures include amniocentesis, CVS, blood test, and bone marrow biopsy.

Consult your doctor or genetic counselor for guidance before taking a karyotype test.

Was this helpful?
5
Medical Reviewer: Avi Varma, MD, MPH, AAHIVS, FAAFP
Last Review Date: 2022 Mar 28
View All Tests and Procedures Articles
THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
  1. Akhtar, F., et al. (2021). Down syndrome. https://www.ncbi.nlm.nih.gov/books/NBK526016/
  2. FAQs about chromosome disorders. (2017). https://rarediseases.info.nih.gov/guides/pages/73/faqs-about-chromosome-disorders
  3. Jee, Y. H., et al. (2017). Genetics of short stature. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5424617/
  4. Karyotype. (n.d.). https://www.genome.gov/genetics-glossary/Karyotype
  5. Milani, D. A. Q., et al. (2021). Genetics, chromosome abnormalities. https://www.ncbi.nlm.nih.gov/books/NBK557691/
  6. Nuchal translucency scan. (n.d.). https://fetalmedicine.org/fmf-certification-2/nuchal-translucency-scan
  7. Ozkan, E., et al. (2021). Genetics, cytogenetic testing and conventional karyotype. https://www.ncbi.nlm.nih.gov/books/NBK563293/
  8. Polygenic trait. (n.d.). https://www.genome.gov/genetics-glossary/Polygenic-Trait
  9. Salomon, L. J., et al. (2019). Risk of miscarriage following amniocentesis or chorionic villus sampling: Systematic review of literature and updated meta-analysis. https://obgyn.onlinelibrary.wiley.com/doi/10.1002/uog.20353
  10. Trisomy 13. (2020). https://rarediseases.info.nih.gov/diseases/7341/trisomy-13
  11. Younesi, S., et al. (2021). Karyotype analysis of amniotic fluid cells and report of chromosomal abnormalities in 15,401 cases of Iranian women. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8484541/