Chromosomes and Fertility

The genetic material of every living thing including your own is contained within the nucleus of cells and is made up of chromosomes. The genes contained in your chromosomes are the blueprint/roadmap for the structure and function of your body (the genetic code for life), and they dictate your sex, appearance, bodily functions, and contribute to your risk of developing certain diseases. Each person has 46 chromosomes made up of 22 pairs of autosomes and one pair of sex chromosomes (X and Y chromosomes). This is called a complete genetic code. We inherit one set of chromosomes from our mother and one set from our father. A normal woman has two X chromosomes and the short hand for her chromosome complement is 46 XX, and a normal man has an X and a Y chromosome which is denoted as 46 XY. A woman's egg contains an X chromosome and the sex of a person/baby is determined by whether the sperm that fertilizes the egg contains an X or a Y chromosome.

Problems with Chromosomes

During the fertilization process an embryo needs the correct number of chromosomes in the proper sequence. Occasionally, the wrong chromosomes are in a fertilized egg. Some of these chromosomal abnormalities have little or no impact on bodily functions, whilst others can have a major impact leading to physical abnormalities and/or intellectual impairment.

There are a number of different types of chromosomal abnormality. Sometimes there is an abnormal number of autosomes. An example of this is Down syndrome where there can be an extra (third) chromosome 21. There can also be an abnormality of the sex chromosomes such as where a woman has one X chromosome instead of two (Turner's Syndrome) or a man has an extra X chromosome as in Klinefelter's Syndrome.

A chromosome translocation is a chromosome abnormality caused by rearrangement of parts between chromosomes. There are two main types of translocation, reciprocal (also known as non-Robertsonian) and Robertsonian. Also, translocations can be balanced (in an even exchange of material with no genetic information extra or missing, and ideally full functionality) or unbalanced (where the exchange of chromosome material is unequal resulting in extra or missing genes).

Many illnesses/abnormalities are inherited by disorders of a single genes that would not be detected by routine testing of the chromosomes. One example of this is cystic fibrosis. If you have a family history of such an inherited condition it may require more specialized testing to see if an abnormality in your genetic material can be found. Therefore, it is important to realize that chromosome testing will not find all possible types of genetic abnormality.

When to do Chromosome testing

Situation when you and/or your partner may have an increased risk of carrying a chromosomal abnormality include;

a low sperm count
prolonged unexplained infertility
multiple (recurrent) miscarriages (three or more)
certain problems encountered during IVF treatment
a family history of babies being born an abnormality

Under those circumstances your fertility specialist may recommend having your chromosomes tested.

Chromosome Analysis

A chromosome analysis is a test that can be performed to determine the number, order and shape of chromosomes. Chromosome analysis is also called karyotyping, which is done by collecting a sample of cells, such as white blood cells from a blood sample. The term karyotyping refers to "karyo" which is the fact that the nucleus of the cell is studied, and "type" which is the fact that the test is a characterization, or analysis of the character. Put together it means a characterization of the cell nucleus. Chromosomal abnormalities that can be tested during a chromosome analysis include those abnormalities described above;

extra chromosomes
missing chromosomes
deletions or additions to the data within each chromosome
translocations of chromosomes (in which all chromosomes are present but rearranged).

When will my test results be ready?

Chromosome testing is a complex laboratory procedure that can take anything between 7 days and three weeks to be ready from the time that the laboratory has your obtained blood sample.

What will happen if my test result is abnormal?

If you test positive for a chromosome abnormality, the next step would usually be to recommend referral to a genetic counsellor or medical geneticist. These specialists are experts in chromosomal abnormalities and inherited conditions and they will be able to explain your test results, answer questions and discuss treatment options with you. Most of the time chromosomal abnormalities cannot be fixed, however, for many abnormalities fertility treatment is available using a technique called Preimplantation Genetic Diagnosis or PGD for short. For more information on this subject please refer to the Bubtree webpage on PGD.