What are karyotype tests?

What are karyotype tests?

What are karyotype tests?

Karyotype tests look closely at the chromosomes inside your cells to see if there is anything out of the ordinary. They are often done during pregnancy to check for problems with the baby. This type of procedure is also called genetic or chromosome testing or cytogenetic analysis.

When you are pregnant, your doctor may do several prenatal screening tests to check for certain genetic and chromosomal disorders. You will probably be offered one in the first trimester and another in the second trimester.

Most women get results that are within the normal range and do not require further testing. But if any of your screening tests show signs of problems, your doctor will suggest follow-up testing so you can know for sure if your growing baby has genetic or chromosomal problems.

Uses for karyotype testing

Humans have 46 chromosomes. Babies inherit 23 from their mother and 23 from their father.

Sometimes babies have an extra chromosome, a missing chromosome, or an abnormal chromosome. Karyotype tests will show if any of these events happened to your child. The most common things doctors look for with karyotype tests include:

  • Down syndrome (trisomy 21). The child has an extra third chromosome 21. This affects his appearance and his learning.
  • Edwards syndrome (trisomy 18). The child has an extra 18th chromosome. These babies usually have many problems and most of them do not live more than a year.
  • Patau syndrome (trisomy 13). The child has an extra 13th chromosome. These children usually have heart problems and severe mental impairment. Most will not live more than a year.
  • Klinefelter's syndrome. The boy has an extra X chromosome (XXY). They may go through puberty more slowly and not have children.
  • Turner syndrome. The girl has a missing or damaged X chromosome. It causes heart problems, neck problems, and short stature.

Karyotype tests can be used for more than just detecting birth defects.

If you have had difficulty getting pregnant or have had multiple miscarriages, your doctor may want to check to see if you or your partner have a chromosome problem.

  • You can find out if you have a disorder that you could pass on to your child.
  • They can test a stillborn baby to see if there's a genetic problem.
  • They can find the cause of certain physical or developmental problems in your child or young child.
  • Chromosomal testing can show if a newborn is a boy or a girl in rare cases where it is not clear.
  • Some cancers can cause chromosomal changes. Karyotype tests will help you choose the right treatment.

Types of karyotype tests

Karyotype tests can only be done during certain weeks of pregnancy. Your doctor will suggest a karyotype test that is right for you based on the stage of your pregnancy and your risks.

Your baby is more likely to have chromosomal problems if:

  • You’re 35 or older.
  • You have another child or a family member who has a chromosome disorder.
  • You or your partner have something unusual in your chromosomes.
  • You have a history of miscarriages or had a baby that was stillborn.

Tests include:

Chorionic villus sampling. Doctors use a long needle to take a small sample of your child's cells from the chorionic villi, which are tissues in the chorion.

Doctors send these cells to a lab for further testing. The results can show if your child has Down syndrome, trisomy 13, trisomy 18, or other genetic problems.

If your doctor says you need to take a chorionic villus sampling, you can do so at 10-13 weeks. There is a possibility that this could lead to a miscarriage. This happens to 1 in 100 women who take the test. There is also a risk to the baby, so doctors only recommend it if there's a good chance your baby has a problem.

Amniocentesis. Doctors get samples of your baby's cells by taking a small amount of amniotic fluid (the fluid that surrounds your baby in the womb) with a long needle that they stick into your abdomen. They send the cells to a lab for further testing.

The results of the test can show if your child has any genetic problems that can be detected by analysis of chorionic villus samples, as well as certain neural tube defects, which are serious problems that can affect your child's brain or spine.

If your doctor says you need an amniocentesis, you can do it between 15 and 20 weeks. There is a chance of miscarriage, but it is less than with a chorionic villus biopsy. This only happens to 1 in 200 women who have the procedure.

Bone marrow aspiration and biopsy. If you are having a chromosome test because of cancer or a blood disorder, your doctor may need to take a sample of your bone marrow. They usually take it from the thigh bone with a special needle when you are numb but awake.

Risks of karyotype testing

The procedures used to collect cells for karyotype testing carry certain risks. Chorionic villus sampling or amniocentesis can cause miscarriage. You may also have heavy bleeding or infection from aspiration and bone marrow biopsy.

Karyotype test results

When the lab returns your results, they have examined your child's chromosomes. So the results are final: either your child has a genetic problem or it doesn't.

This is different from earlier screening tests, which could only tell if the risk of a problem was high or low. Your doctor will discuss the test results with you.


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