Basics of Genetic Testing in Infertility: Karyotype
A Karyotype is a test that looks at an individual’s DNA. This is a very useful test for diagnosis of several conditions such as recurrent pregnancy loss, some patients with diminished ovarian reserve, certain patients with low or absent sperm, and for presumed disorders of sexual differentiation.
A genetically normal individual will have 23 pairs of chromosomes (see image for a normal, genetically female karyotype). A karyotype determines if you have a normal number and arrangement of chromosomes through microscopic evaluation. A karyotype can detect deletions and duplications that are 5 megabases (or 5 million base pairs) or greater. This illustrates that like all tests it is a powerful tool but is not perfect.
To perform a karyotype, live cells need to be grown in culture to perform this test. Therefore, sometimes a karyotype cannot be done on products of conception (the tissue that we test if someone has a miscarriage). If there are not live cells present in the specimen, we will not be able to perform a karyotype. In this case, we can often use an alternative testing method, which we will not describe in detail, called a microarray to attempt to identify a genetic defect.
A karyotype will only answer the genetic profile of the individual tested. If we test products of conception, it does not tell us about the mother and father. Therefore, depending on the clinical scenario, both partners may need to be tested.
As a clarification, each of these tests look at different things. A karyotype is very different from carrier screening. It is also very different from PGT-A, which will discussed in the next post, and other testing modalities which we will address in the future.