Karyotype

Karyotypes are used to identify chromosomal causes of infertility

Around 10% of infertility issues are caused by chromosomal abnormalities. Identifying the reason for the issue means we can propose the most appropriate course of treatment for ensuring a pregnancy.

What is a karyotype?

A karyotype is a person’s set of chromosomes. Human beings have 46 chromosomes (23 pairs). One of those pairs is the one that differentiates between the two sexes (XY for males and XX for females). Chromosomes contain a person's complete genetic information. Therefore, a karyotype is nothing more than the way in which that information is organised and arranged.

What is a karyotype used for? What is its purpose?

The chromosomes in each species have a specific structure both in terms of shape and in terms of size like personal banding when they are stained in the laboratory. This makes it possible to identify them and to understand if all the genetic information is present and if it is present in the correct order.

Obtaining a person's karyotype allows us to understand if that person has all the genetic information that is found in human beings or if he or she has any kind of excess or defect. It also tells us if it is appropriately arranged or, in other words, if each chromosome maintains its structure. Abnormalities both in the structure and in the number of chromosomes can lead to fertility issues.

What does obtaining a karyotype entail?

A blood test needs to be done in order to obtain a karyotype. A blood sample is used in the laboratory to generate lymphocyte culture. The chromosomes use it to compact as much as possible, making it possible to identify their number and structure under the microscope. Once they have been observed under the microscope, it is possible to know if there is any kind of numerical or structural abnormality.

When is obtaining a karyotype advisable?

This test is very important in patients who need to make use of an assisted reproduction technique because there is a greater chance of chromosomal abnormalities amongst couples with reproduction issues compared with the general population. It is particularly recommended when a patient has a severe semen abnormality, ovarian failure, sterility of an unknown cause or long-term sterility, and also for couples who have had recurrent pregnancy losses or implantation failures following IVF treatment.

What are the most common abnormalities amongst patients with fertility issues?

The most common chromosomal abnormalities in these patients include numerical abnormalities such as Klinefelter syndrome (47,XXY karyotype) or Turner syndrome (45,X0 karyotype). They can also be structural chromosomal abnormalities (Robertsonian translocations, inversions, duplicates, etc.). Structural abnormalities can make getting pregnant difficult because they cause abnormalities in the seminogram in men and ovarian failure in women. It can also cause recurrent pregnancy loss or implantation failure, irrespective of if the pregnancy was natural or as a result of in vitro fertilisation treatment.

What happens if there is an abnormality in the karyotype?

If a chromosomal abnormality in one of the partners is detected, the solution for ensuring biologically healthy offspring is CCS (comprehensive chromosome screening) performed on the embryo. CCS can be used to detect changes in the quantity of all the embryo's chromosomes. Therefore, it is possible to select the embryos that do not have the abnormality in question and guarantee a successful pregnancy and the birth of a healthy child.