Karyotype – Pregnancy

Chromosome abnormalities can be screened for by NIPT (non-invasive testing). Only an invasive test can confirm the high risk result from a screening NIPT test.

Invasive testing includes chorionic villus sampling or amniocentesis.

The type of invasive test performed will depend on the findings at NIPT and/or ultrasound findings from a morphology scan.

There are 3 methods of testing depending on the clinical indication:

  1. Conventional banded karyotype – for sex chromosomes disorders, common aneuploides, unbalanced chromosome rearrangements, balanced chromosome rearrangements or suspected mosaicism.
  2. Microarray – this detects gain or loss of genetic material that is smaller than that which can be detected by a banded karyotype and covers all chromosomes. It cannot detect balanced rearrangements. It is indicated if there are structural abnormalities detected by ultrasound.
  3. FISH (fluorescence in situ hybridization) is used for microdeletion syndromes and is a rapid method of testing for common chromosome trisomies.


At least 60% of first trimester miscarriages are due to a chromosome abnormality, the majority of which are not inherited. Karyotyping the miscarriage material will be able to give an answer for the pregnancy loss in 60% of cases. Follow up genetic testing of the parents will be indicated in a small number of these cases.

Miscarriage material can be tested by conventional karyotype and if this fails microarray. Conventional karyotype helps in cases where there is a balanced structural rearrangement (which array cannot detect) as well as extra or missing genetic material.

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