“Good morning Bill. Should we have PGS testing performed on our embryos? The Guide says it improves the viability of embryos for transfer, but I’ve read that PGS is a risky process because it can damage or destroy embryos.” — Palmer
Thanks for the message Palmer.
In general, I don’t recommend that every embryo be PGS tested before being transferred, but this often depends on the clinic and the lab performing the analysis. For some cycles, PGS is absolutely necessary, especially for couples that have a history of failed pregnancies or miscarriages. For other couples with no such history, PGS isn’t warranted and can add risks and costs to your program.
It’s true that PGS testing can damage some embryos. Most genetic labs won’t disclose how great is the risk, but I suspect that about 2 in 10 embryos may be damaged during the process. Some embryos may be very damaged or destroyed. If your IVF resulted in very few embryos, you should skip PGS, so you don’t risk losing any unnecessarily. (By the way, an experienced, highly qualified labs will keep your embryos safer — so also consider the quality of your clinic.)
But PGS can often save more embryos than it harms.
PGS Testing Basics
Remember some basic high-school biology… Chromosomes come in 23 pairs, and sperm and egg cells each provide a strand of each pair. When one sperm combines with one egg, they combine their chromosomes to form one complete set.
When one of those 23 chromosomes is out of place (missing, added or switched with another) the result is a chromosomal disorder like Downs Syndrome. (Note that Downs Syndrome is different than a genetic disorder because it caused the absence or presence of an entire chromosome, not just a single gene.) PGS will detect a missing or extra chromosome, and so the possibility of Downs Syndrome and similar conditions.
Also importantly for many couples is that PGS also will identify any chromosomes that may be damaged or incomplete, which often results in miscarriage or failed pregnancy.
Studies suggest that 75% of early-stage miscarriages and failed pregnancies are caused by problems with the embryos’ chromosomes (many of which could have been detected by PGS). So PGS testing can significantly improve your pregnancy rate. It can also cut thousands of dollars from your budget by reducing the number of repeat FET cycles needed to get pregnant.
Remember chromosomes are long strands of thousands of amino acids in very specific sequences. When sperm & eggs combine, it’s possible for some chromosomes to end up in the wrong place. It’s also possible that the strands can get twisted, tangled or damaged. If either happens, the embryo will not have the information it needs to develop normally. PGS will detect most of these cases and head off the failed pregnancy.
Think of the embryo like a delivery truck… Even if the truck is running well, the cargo it’s carrying may be spoiled and useless. The only way to know if the cargo is good is to open the truck and check what’s inside. Similarly, you can’t tell if an embryo can develop into a healthy fetus just because it’s healthy and well developed. You need to check the chromosomes themselves – and that’s what PGS does.
Who Should Get PGS Tested?
Damaged or mixed up chromosomes are quite common. Every IVF cycle will result in a few embryos that have poorly formed or incomplete chromosomes. This is true even for young, healthy egg and sperm donors — although the younger the donor the more healthy the embryos are likely to be. So it is true that PGS is less important if the donors are both young and have a proven fertility history.
Older couples typically see more chromosomal damage in their IVF cycle. Other factors like lifestyle can also increase the expected level of damage. So couples who may be older or who may have been exposed to unhealthy environments (such as drug use) should definitely consider PGS. So should any couple that has had previous unexplained failed IVF or pregnancies.
But very importantly, even a healthy individual with no previous genetic disorder will have some chromosomal problems. Some studies show that damage can appear in about 50% of an otherwise healthy person’s IVF embryos. So even some young couples might consider PGS analysis to detect and remove any damaged embryos.
In the case of PGS for Gender Selection… on average you can assume half of your embryos will be boys, and the other half girls. So if you limit yourself to boy embryos only, you will reduce the number of embryos for transfer by 50%. However it is also possible that more than half of the embryos are the “undesired” gender, and your final embryos will be reduced more dramatically. (So even if you prefer boys, it is always smart not to discard any embryos based on gender, because you may find that girls are your only option if you want a successful pregnancy.)
Every case is different, but the final decision should be balance the cost of the PGS testing (usually about $5000 USD) against the risk factors for the specific couple. In some cases it may be a good investment; while in other cases it’s just a way of buying some peace of mind.
Some Basic High School Biology
For those of us who were sleeping in high-school biology, here are some additional basics about genetics to help understand the details of PGS:
• All cells contain DNA, which are the blueprints for making more cells, and (all combined) all living creatures. DNA is made up of just a few types of molecules called Amino Acids, which combine in a myriad of different ways to create all the possible attributes of living things.
• A gene is a portion of DNA that has the instructions for combining Amino Acids into a specific protein. Human beings have over 22,000 genes in total. Genes carry the instructions for everything from how to build your heart to the color of your eyes. Damaged genes also carry instructions for hereditary illnesses, like Parkinson’s or Hutchinson’s disease.
• Within your cells, individual genes are grouped together into 23 pairs called chromosomes. Each chromosome has many genes.
• A chromosome is simply a very long piece of DNA that cells can easily copy. Humans usually have 23 pairs of chromosomes. They are numbered 1-22 with the 23rd pair being either XX in girls or XY in boys.
• Chromosomes are copied and passed along from cell to cell when they divide, including sperm and egg cells. When a new fetus is conceived, half the chromosomes from the sperm donor are combined with half the chromosomes from the egg donor, to provide a full group of chromosomes that share some traits with each parent, but not all. PGS testing will make sure that all those chromosomes are present and healthy in each embryo.
I hope this is useful,
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