The choice of which tests to do depends on a multitude of factors:

​

a) the reason (or indication) for doing the invasive test.  These could include ultrasound abnormality in the fetus [e.g. increased nuchal translucency (more detailed testing may be required if the nuchal translucency exceeds 4.5 mm), multiple ultrasound abnormalities, isolated ultrasound abnormalities), positive family history or past history of a known genetic disorder, positive family history or past history of a severe abnormalitiy where a genetic disorder has not been excluded yet.

b) the level of resolution of the genetic test desired by the couple. The result of the genetic test may or may not affect the couple's plan for the current pregnancy or plan for future pregnancies.  Where the results of the tests do not affect decisions for this or future pregnancy, then the test is not required.  Some couples may choose to know only if the fetus is affected by the common major chromosomal abnormalities (QF-PCR and / or karyotype may be enough), pathogenic copy number variants involving more than 50,000 bases (chromosomal microarray test), all type of chromosomal abnormalities but not genetic disorders involving less than 50,000 bases (karyotype and chromosomal microarray test), and most chromosomal abnormalities and most genetic syndromes (chromosomal microarray and whole exome sequencing).  None of the genetic tests allows detection of all genetic diseases. 

For any of these tests, patients can choose to cancel the test before the results are released to them if they change their initial decision to have the test.  Where the fetus is diagnosed to have a genetic disorder, it may affect the future insurability and employment of the child.