Chromosome genetic testing can play an important role in in-vitro fertilisation (IVF), helping to reduce the risk of miscarriage, especially in older women, and maximising the chance of a successful pregnancy.
Pre-implantation genetic testing for aneuploidy (PGT-A) is a screening process that takes place prior to the implantation of embryos.
It allows an embryologist to test embryos for chromosomal abnormalities, to help identify those with the best chance of developing into a healthy pregnancy.
“When a sperm fertilises an egg, the embryo should result in having 23 pairs of chromosomes, that is, one from the egg and one from the sperm in each pair, for a total of 46 chromosomes,” explains Dr Bart Kuczera of Beacon Care Fertility in Dublin.
“The PGT-A test can help identify embryos carrying this number of chromosomes and therefore the best chance of developing into a healthy pregnancy. An embryo that doesn’t have the correct number of chromosomes will most likely fail to implant and if it does implant, it will most likely miscarry.”
Prior to its development as a selection tool, embryo grading was done on the basis of the embryologist’s trained eye, looking to identify those embryos fittest for the journey ahead by sight alone.
With PGT-A, fertility clinics have the potential to improve IVF success rates by identifying embryos with the correct number of chromosomes. Not every embryo does. In fact, between 40 per cent and 75 per cent of human embryos contain an abnormal number of chromosomes, with the chances of it occurring increasing with the woman’s age. Most such embryos will not implant and if they do, are most likely to miscarry.
The screening procedure involves taking sample cells from each embryo, which are sent to a genetics laboratory for testing. The process can take two to three weeks, and in the meantime the embryos are frozen, until the results come back. The selection is then made for embryo transfer, usually one at a time.
Success rate
A recent American study found that women undergoing IVF achieved a 95 per cent pregnancy success rate over the course of three consecutive frozen embryo transfers when utilising embryo viability screening (PGT-A) to select the best embryo to transfer.
More than 4,000 women with a median age of 35.4 years took part in the retrospective study from the RMA clinic in New Jersey, as reported by the European Society of Human Reproduction.
Beacon Care Fertility and its Care partners pioneered this highly specialised technology. In a six-month period, Beacon Care Fertility’s embryologists screened a total of 411 embryos and obtained a result for 393 embryos, meaning 95.6 per cent of its embryos had a diagnostic by the end of the PGT-A process.
This kind of screening may be of particular benefit to women with a history of repeated miscarriages or who have had failed IVF treatments previously, as well as older women.
The study concluded that recurrent implantation failure was rare and more likely to be embryonic in nature than endometrial.
Chromosomal abnormality is a major factor in failure of embryos to implant, so screening all 23 chromosomes and transferring only the embryos with the correct number of chromosomes can significantly improve the chance of a successful pregnancy.
Female age
The most common factor for unsuccessful IVF is female age. This is due to the increase in chromosomal abnormalities in eggs and subsequently embryos as women get older.
The average age of Dr Kuczera’s patients at Beacon Care is 38, which means many women are over 40. Using the PGT-A screening process as a selection tool can’t alter the quality of the eggs, but it can save time by ensuring those embryos with the best possible chance of survival are the ones selected for implantation.
Whereas appearance was always the standard indicator embryologists used to grade embryos, the PGT-A test is determined by science.
Not alone does can it improve your chances of a successful pregnancy, but “it can also buy you more time,” says Dr Kuczera.
“So if you are 41 and have seven embryos, by the time you go through them, it could be half a year’s time. That means you are half a year older by the time you need another egg collection, at a point when time is of the essence. With this, you can change the whole tactics.”
