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Section 14 – What is a single nucleotide polymorphism array (SNP) test?


This test is offered only when there are certain structural changes seen on an ultrasound scan.

A single nucleotide polymorphism array (SNP) is a test that looks at the chromosomes in the cells in the amniotic fluid or chorionic villus sampling (CVS) or amniotic fluid sample. The test looks for small changes in genetic material. A change in this genetic material may explain the cause of the abnormalities seen on the ultrasound scan.

The SNP array test:

  • will not detect changes in single genes, such as cystic fibrosis (each chromosome contains thousands of genes)
  • may identify a chromosomal change that may not be related to the findings identified on the ultrasound scan (these changes may have implications for the future health of your baby or other members of your family), and
  •  may show some chromosomal changes that have an unknown effect on your baby.

This test looks for chromosomal changes in more detail than the QF-PCR or karyotype test.

SNP array test results

These results are usually ready within about 14 calendar days.

Sometimes it takes a bit longer to complete these tests (this does not mean there is more chance of a problem with your baby).

Occasionally, in about 0.4% (1 in 250) of tests you will not get a result. If this happens, you may be offered another amniocentesis.

In some cases an SNP array test may give a result that is not clear. Your obstetrician will discuss this with you if this happens.

The SNP array 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.