Each one of us has a genetic blueprint — an ‘instruction manual’ that makes us uniquely human and determines our individual characteristics. This blueprint is contained in every cell of our bodies and is packaged into structures called chromosomes. Normally, there are 46 chromosomes — 23 are inherited from the mother and 23 are inherited from the father.
During conception, chromosomes from the mother and father may combine incorrectly, resulting in an abnormal number of chromosomes in the embryo. In most circumstances, an abnormal number of chromosomes is incompatible with life. If these abnormal embryos are transferred, they fail to implant successfully or miscarry. However, some abnormal embryos can carry through to birth and result in a baby with a chromosomal disorder — the most well-known one is Down Syndrome.
PGT-A involves taking a biopsy of the embryo after it has grown and developed for 5–6 days. We take 5–7 cells from its outer layer that would otherwise be destined to form the placenta. From this sample, we can predict the number of chromosomes present in each cell, allowing us to determine whether the embryo is likely to be normal or abnormal. This information guides our decision on the best embryos to transfer, which helps prevent the transfer of embryos that may result in unsuccessful transfer, miscarriages, or babies with chromosomal abnormalities.
The percentage of embryos with abnormal chromosomes on Day 5 increases with maternal age.
At first glance, conducting PGT-A on every embryo may seem beneficial. However, there are a few limitations that prevent its non-selective use:
Embryos are fragile, so any procedure that involves handling the embryo and disturbing its surrounding conditions poses the risk of harm. However, while the risk of harm will always exist, it is thought that the overall risk of damage to the embryo is minimal. The level of risk is also related to how well the biopsy is conducted, which is why we have experienced and skilled scientists on hand to perform these procedures.
When we conduct testing on a sample of cells from the embryo, we are assuming that this sample is representative of all the cells in the embryo. However, this may not be true – a condition called mosaicism may exist, where some of the embryo’s cells have an abnormal number of chromosomes and some have a normal number. Embryos displaying mosaicism can still result in a healthy, live birth. Therefore, the test may cause us to discard embryos that have the potential for a successful, ongoing pregnancy. To help avoid this, we also assess the level of mosaicism in the embryo. This gives patients the option of still proceeding with a transfer if the embryo only displays a low level of mosaicism. On the other side of the coin, a normal PGT-A also does not guarantee that the embryo has a normal number of chromosomes. In the setting of a normal test result, we still recommend patients undergo antenatal screening.
The results of the genetic testing may return as ‘indeterminant’, meaning the test could not determine whether the genetic material of the embryo was normal, or abnormal. This may occur for a variety of reasons, including a poor-quality embryo.
We generally recommend PGT-A for certain groups of people, including those who:
Your Newlife fertility specialist will take the time to understand your personal situation and preferences, before helping you to decide if PGT is right for you.
At Newlife IVF, preimplantation genetic testing currently costs $699 per embryo.*
*Fee correct as of 1 August 2019.
Fertility specialist Dr Nicole Hope discusses the process of donating your eggs and the important factors to consider before you donate.Learn more
In this article, we discuss the fertility treatments available for lesbian and gay couples, including donor eggs and sperm, and surrogacy.Learn more
What is endometriosis? In endometriosis, tissue similar to the lining of the uterus (known as the endometrium) grows on organs and tissues outside the uterus. It typically affects the ovaries, fallopian tubes and the tissue...Learn more