A surrogacy journey opens you up to a wide new world; you will be introduced to your surrogate partner and agency team, committed to being by your side throughout, and meet an online community of fellow intended parents experiencing the same journey ups and downs as you are. The biggest learning curve though, comes from studying the fascinating field of In Vitro Fertilization (IVF). You will find out all about embryo creation, as well as pick up a whole new vocabulary. Sound exciting? It is. But unless you hold a medical degree, it can also be a bit confusing.
Treating infertility is emotionally depleting and expensive, but one of the definite advantages of IVF is that it can provide options to help you bypass certain hurdles to pregnancy that natural fertilization can’t; such as genetic testing at the embryonic level. You’ve undoubtedly already spent a lot of time researching and may feel drained at the prospect of deciphering complicated IVF diagrams and explanations. Genetic testing and it’s lingo is one of the most difficult areas for intended parents to get straight, so read on for a cheat-sheet on what it means and whether it’s worth considering embryonic screening for your surrogacy journey.
Get a handle on the terminology
Chromosomes are important because they contain the information that instructs the body’s cells how to function. They are string-like structures found in the centre (nucleus) of cells. A human cell typically contains 46 chromosomes. An embryo receives 23 chromosomes from the sperm and 23 from the egg. Twenty-two of those are matching pairs called the autosomes, while the twenty-third pair are called the sex chromosomes, and they are most commonly either XX or XY.
Aneuploidy is the occurrence of extra or missing chromosomes leading to an unbalanced chromosome complement. Chromosomal aneuploidy in an embryo can result in implantation failure, pregnancy loss or syndromes such as Down’s, Edward’s and Patau’s. An embryo with a normal number of chromosomes is called euploid , while one with an abnormal number is called aneuploid.
X-linked disorders are caused when there is a mutation in a gene on the X sex chromosome. (eg. Hemophilia; Duchenne Muscular Dystrophy)
Autosomal diseases occur when there is a mutation in a gene on one of the autosomes.
• Autosomal dominant diseases: (Eg. Marfan syndrome; Neurofibromatosis type 1) • Autosomal recessive diseases: (Eg. Cystic Fibrosis; Sickle Cell Anemia)
What is Preimplantation Genetic Testing (PGT)?
The name for all testing at the embryonic level is Preimplantation Genetic Testing. PGT is performed before embryo transfer, or ‘pre-implantation’, so as to increase the chance for your medical team to select a healthy embryo, that will then develop into a healthy baby.
PGT consists of a few different testing options but the goal of these screenings is either:
- To be able to select an embryo without a known or suspected gene problem or defect (detected by PGT-M aka. PGD)
- To be able to select an embryo without an abnormal number of chromosomes (detected by PGT-A aka. PGS)
* It’s important to qualify that Preimplantation Genetic Tests are not 100% accurate. They cannot guarantee you’ll have a chromosomally healthy baby and they don’t replace the prenatal screenings your surrogate partner (and all pregnant people) pass through. Most birth defects are not related to missing or extra chromosomes and aren’t genetically based; some aren’t detectable before implantation or even during pregnancy.
In case it wasn’t confusing enough…
Just when you thought you were on top of things, PGT testing options were recently renamed. Tests formerly known as PGD and PGS have been canceled and are now replaced by new terminology in The International Glossary on Infertility.
• PGD testing for single gene defects is now called PGT-M
• PGS testing for aneuploidies is now called PGT-A and for chromosomal structural
rearrangements is called PGT-SR.
* It will likely take several years for the new names to really catch on, so for now either
What is PGT-A (pre-implantation genetic testing for aneuploidy) / formerly known as PGS
Pre-implantation genetic testing for aneuploidy (PGT-A) is a screening test for extra or missing chromosomes.
The goal of PGT-A testing is to identify any embryos with aneuploidy so you have the option to transfer an embryo that has the correct number of chromosomes and increase the odds of implantation.
You should consider PGT-A if:
- You are a woman 35 years old or above (aneuploidy risk increases with age)
- You have had a history of miscarriage or recurrent IVF failures
- You have severe male factor infertility
- You have a very large number of embryos
- Determining gender is of importance
- A small amount of damage can occur when the embryo is biopsied to remove cells for testing
- Mosaicism ( a condition where some of the cells in a generally normal embryo are abnormal or some of the cells in a generally abnormal embryo are normal) can lead to test results that do not accurately reflect the chromosome status of the embryo
What is PGT-SR (pre-implantation genetic testing
for structural rearrangements) / formerly known as PGS?
Pre-implantation genetic testing for structural rearrangements is a screening test for intended parents with known chromosomal rearrangements or translocations (where a piece of one chromosome breaks off and attaches to another chromosome resulting in a gain or loss of a cell’s genetic material). Embryos can be tested to determine if they contain the correct amount of genetic information. The aim of PGT-SR is to provide intended parents the opportunity to decrease the odds of miscarriage.
You should consider PGT-SR if:
- You are a known carrier of a balanced chromosomal translocation
What is PGT-M (pre-implantation genetic testing for a monogenic disease) / formerly known as PGD?
Pre-implantation genetic testing for a monogenic disease (PGT-M) is a screening test for intended parents who carry a genetic mutation of some kind or who have a family history of genetic disease, and worry about passing it to their offspring. The aim of PGT-M is to provide intended parents the opportunity to prevent transferring an embryo affected by a specific disorder.
You should consider PGT-M if:
• You have, or have in your family, specific genetic diseases including X-linked, autosomal recessive and autosomal dominant diseases
• You need to match stem cells for other siblings in need of a bone marrow transplant
• Determining gender is of importance
What is Gender Selection?
Preimplantation Genetic Testing options offer a much higher chance of having a child of a preferred gender. There are some diseases which are much more common in males or in females, so avoiding having a child of that gender can reduce the odds of these conditions.
Gender selection involves using PGT-A or PGT-M techniques to determine X and Y chromosomes; thus, genetic gender. Identifying gender allows the transfer of only male or female embryos accordingly.
What are the steps involved in Preimplantation Genetic Testing (PGT)?
Biopsies are typically taken when your embryos have reached the ‘blastocyst stage’ (5 to 6 days after fertilization) but can also occur on day 3. The embryologist will biopsy 3-8 cells, removing them from the outer layer of the embryo using a high- powered microscope. The biopsy process does not harm the embryo; they are then frozen and safely stored in the clinic.
The biopsied cells from your embryos are sent to the lab to be tested.
The lab will examine and assess the cells from your embryos.
After a biopsy is taken and laboratory tests are performed, it typically takes 7-14 days to receive your results. Testing results will be sent to your IVF team and passed on to your personal coordinator, who will inform you.
5. Embryo Transfer
After you have reviewed and discussed your embryos’ testing results, you and your IVF team can determine a suitable embryo and move to the embryo transfer stage.
What are some risk factors for chromosomal disorders?
- The leading risk factor for chromosomal disorders is maternal age. If a woman is 35 years old, or older, at the time of delivery, the baby is at a higher risk for a genetic disorder. A woman is born with all the eggs she will ever have, which mature during puberty. As she ages, not only do her eggs age, but her number of viable eggs decrease.
- A lesser risk factor for the development of chromosomal abnormalities, is the way in which a woman processes folic acid. New research suggests that women
who have difficulty processing folic acid may be predisposed to having a child with chromosomal abnormalities. This risk can be easily reduced with the consumption of prenatal vitamins during pregnancy.