Saltar al contenido
Genetics in Fertility
Genetics are a contributing factor in up to 10 percent of couples who experience infertility or recurrent pregnancy loss.
Genetic testing is a type of medical test that identifies changes in chromosomes, genes, or proteins. The results of a genetic test can confirm or rule out a suspected genetic condition or help determine a person’s chance of developing or passing on a genetic disorder (taken from www.23andme.com).
Specialists in Reproductive Medicine might find some blockages along the road when it comes to genetics. It might change a lot. Genetics can be friends or foe. And how much can we rely on them?
Diseases and chromosomic alterations can be evident and related to recurrent failures with in vitro fertilisation. Today, DNA analysis has been offered as a very useful tool to diagnose diseases we could not detect easily before on patients. In occasions, they were detected late in the pregnancy or after analysing samples of a miscarriage. However, it is undeniable that genetic testing is here to stay and to keep evolving.
With genetic testing we are able to check DNA integrity and possible diseases, alterations or mutations that can be present. It can work as a powerful tool to future parents when it comes to decide which treatment is more convenient, depending on the medical and family history.
Human’s karyotype it is composed of 23 pairs of chromosomes, for a total of 46 chromosomes in each cell.
From this 23 pairs we do have 22 pairs called autosomes and 1 pair called sexual chromosomes (X,Y). A change in the number of chromosomes can cause problems with growth, development and function of the body’s system. These changes can occur during the formation of the reproductive cells (egg and sperm), in early fetal development, or in any cell after birth. A gain or loss of chromosomes from the normal 46 is called aneuploidy. This is due to a sporadic event of nondisjunction (non-division) of chromosomes.
A common form of aneuploidy is trisomy (presence of extra chromosome in the cells). An example is Down syndrome, which has an extra chromosome 21. Monosomy is the loss of one chromosome in the cells. Turner syndrome is an example, where we find an absence of the X chromosome in women.
Each chromosome has three parts. The top (short part) named p arm, the middle called centromere, and the bottom called q arm (long part).
In the male we can find infertility factors associated with genetic risks, like non-obstructive azoospermia, oligospermia and the congenital absence of the vas deferens (bilateral or unilateral). These factors carry a risk associated with chromosome abnormality and microdeletion of the Y chromosome.
In women, it is important to be aware that age is the most significant cause of infertility in our medical practice. The chances of conceiving a normal, healthy child decrease with age. When a 30 year old woman has approximately a 20% chance of conceiving each month, a 40 year old woman has 5% chances. Genetic testing can be used at any stage of life. From the embryo to the very old age.
The greater the age, the greater the chances to have fetal chromosomic alterations. Women over the age of 40 should consider genetic testing together with their FIV/ICSI procedure.
It is sensible to advise preimplantation genetic screening or diagnosis for aneuploidy (PGS/PGD), and prenatal screening and diagnosis of fetal aneuploidy, for women over the age of 40 or with family or personal history of chromosomic disease. The prenatal screening includes the non-invasive tests: maternal serum screening, nuchal translucency ultrasound and noninvasive prenatal testing of fetal DNA in maternal blood. And the invasive ones are the chorionic villus sampling (taken at 10-12 weeks of gestation) and amniocentesis (taken at >15 weeks of gestation).
These test are a help also for women with recurrent miscarriage. Data has shown that 60% of pregnancies lost from couples with 2-4 miscarriages are chromosomally abnormal (Ogasawara et al., 2000), and 76% of embryos are chromosomally abnormal for patients with >3 miscarriages (Pellicer et al., 1999).
There is another diagnose associated with genetic risk in women called the primary ovarian insufficiency. It will present with elevation of the FHS hormone in women under 35 years. Usually happens between 40 to 50 years (menopause). In this condition happens before that age it has been associated with the FMR1 gene (X-chromosome).
The following data taken from the American Society for Reproductive medicine (ASRM) shows the rate of reduction in pregnancy loss after preimplantation genetic diagnose.
This following data shows the percentage of abortion rate versus take-home babies with and without preimplantation genetic testing.
In conclusion, genetic testing has a lot of value when it comes to prevention and study of any anomaly or alterations that can be detected. There is no need to wait for the anomaly or chromosomic alteration to appear. However, genetic testing still not available for everyone because of its high cost and the need to freeze embryos to wait for results, as the case of preimplantation genetic testing.
Scientists and doctors need to be up-to-date with the advances and tools available to diagnose alterations that were almost impossible to detect years ago.
But remember, negative results from genetic testing do not rule out an unidentified genetic etiology.
Thanks to the Genetics home reference website, the American Society of Reproductive Medicine (ASRM), 23andme and the Reproductive Medicine Associates of Connecticut.