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Section 12 - What is a karyotype?

This laboratory test takes longer than the QF-PCR test but will detect more chromosomal changes. It is not done for higher chance screening results from the combined or quadruple test or NIPT, unless these show your baby has Down’s syndrome (T21), Edwards’ syndrome (T18) or Patau’s syndrome (T13). The laboratory will carry out a karyotype test to see if any other babies you may have in the future could have the condition.

To do this test, the cells from your baby that are floating in the amniotic fluid or from the chorionic villus sampling (CVS) are grown (cultured) in the laboratory (this takes about 10 to 14 calendar days). The laboratory staff will examine the cells under a microscope to look for changes in the number and appearance of your baby’s chromosomes.

The karyotype test will not detect:

  • changes in single genes, such as cystic fibrosis (each chromosome contains thousands of genes)
  • microdeletions (loss of small segments of a chromosome), or
  • other small changes in chromosomes.

Karyotype test results

These results are usually ready within about two weeks.

Sometimes it takes a bit longer to complete these tests, and you will have to wait a few extra days. (This does not mean there is more chance of a problem with your baby).

In some cases, a karyotype may give a result that is not clear. Your obstetrician will discuss this with you if this happens.

The karyotype test will show the sex of your baby. If you do not want to know the sex of your baby, please tell your midwife or obstetrician.