Genetics play a pivotal role in reproduction and fertility. Genetic abnormalities can affect the ability of an embryo to grow, implant and develop, resulting in miscarriage or infertility. This section explains the background behind genetics and how it affects miscarriage.
The information that your body needs to tell it how to function and what to look like is all stored in code form in almost every single cell. The "code" is written in DNA (deoxyribonucleic acid), which is made up of 4 different chemical units called bases. The bases are adenine (A), thymine (T), guanine (G) and cytosine (C). The code, if you were to read it, would look something like this:
.CGTAGCTTACTTTAGTCGCTAGCAAACGCATCGAGGCTCGATCAGCGAGTCAGC.
A gene is a small section of the code (though much longer than this example!) that can be decoded by the cell to mean something. A single gene might be responsible for any aspect of your body's function or appearance, like making a certain protein or the colour of your eyes!
Long strings of DNA, containing hundreds of genes each, coil up in the form of chromosomes. It is the chromosomes we can see under the microscope, although individual strands of DNA and genes are far too small to be looked at in this way. Chromosomes are made up of a series of genes, and genes are composed of DNA.
In normal human cells there are 46 chromosomes: 2 sex chromosomes (two X chromosomes for females and one X and one Y chromosome for males) and 22 pairs of autosomes (non-sex chromosomes). When producing sperm and eggs, the cells divide so that there are only 23 chromosomes - one of each pair. At fertilization, the chromosomes from the sperm and egg come together to give the full complement of 46 chromosomes to the embryo.
Genetic mistakesSometimes mistakes can happen in the copying of the code when a cell divides. A section of the DNA can be missed out (a gene deletion): or misread (a gene mutation): In some cases, a whole chromosome can end up in the wrong cell, so that the cell has the wrong number of chromosomes (aneuploidy). Sometimes a piece of one chromosome can get stuck onto another one (translocation). These mistakes can happen when any cell is dividing. If they occur during the formation of sperm and egg cells, it will affect the genetic makeup of the embryo. It might only result in the child having a slightly different nose, or it could be as serious as missing the gene that codes for the production of a protein essential to growth and survival.
Chromosome rearrangementsSome people have a higher chance than usual of producing eggs or sperm that have mistakes in the chromosomes. If, when you were conceived, one piece of a chromosome was stuck on another, it would not affect you because you would still have all the information you need, just in a different order. But then, when you produce sperm or eggs, which only have half the number of chromosomes as the rest of your cells, the matching chromosome pieces could get separated during the cell divisions. Then the egg or sperm wouldn't have all the information it needs. You could end up with the right combination though, if the sperm or egg receives one of each pair with the rearrangement or one of each pair not rearranged. The wrong complement of chromosomes will usually result in failed implantation, miscarriage or an abnormality in the baby.