As women start having babies later in life, chromosomal abnormalities are becoming a greater concern. Adding to that is the availability of genetic screening, which may allow people to know if there is a problem before the birth of their child. However, it also carries the risk of false positives.
It is important to note that chromosomal abnormalities are not the same as genetic defects. A genetic defect or disease is the result of a specific gene that one or both parents carry, such as the gene for cystic fibrosis. A chromosomal disorder is the result of damage to the DNA instructions carried in an egg or a sperm.
What is a Chromosome?
A chromosome is the structure inside a cell that consists of proteins and DNA. The word chromosome comes from the Greek words for color - chroma, and body - soma. Inside a chromosome is all of the genetic information and material that will direct a cell to develop into a part of the body. Information such as hair color, height and sex is determined by the contents of our chromosomes.
Usually, a person will have 46 chromosomes, ordered in 23 pairs. One half of each pair comes from our mother, and the other from our father. Any alterations or damage done to the number, or structure, of chromosomes will result in a chromosomal abnormality, which can have a serious impact on physical and mental development.
Causes of Chromosomal Abnormalities
A chromosomal abnormality begins in the reproductive tissues of both parents. Eggs and sperm usually have 23 chromosome each, half of the parent’s chromosomes. Occasionally something will go wrong when the chromosome splits and a sperm or an egg can end up with missing pieces of DNA, or there might be extra genetic material. Usually there is no known cause for these abnormalities and therefore nothing can be done to prevent them.
When one of these damaged sperm or eggs join with a normal sperm or egg, the result will be an embryo with a chromosomal abnormality. Usually these embryos do not survive and a chemical pregnancy, or early miscarriage is the result, often without the woman even knowing she was pregnant.
It is estimated that up to 70% of first trimester miscarriages are the result of chromosomal abnormalities.