PGD and PGS
PGD (Pre-implantation Genetic Diagnosis) generally used to detect genetic anomalies where one or both partners of a couple are carriers of a genetic condition. In these instances IVF is performed and the embryos are tested for this specific condition and disease-free embryos are transferred. PGS (Pre-implantation Genetic Screening) entails embryos being screened for chromosomal abnormalities in patients undergoing routine IVF.
Is PGD/PGS right for me?
It is known that the most common reason for IVF failure is chromosomal abnormal embryos. The percentage of abnormal embryos increases with the age of the female patient. Embryos with abnormal chromosomes may prevent implantation or lead to pregnancy loss. If you experience the following, you may benefit from PGS.
Recurrent miscarriage
The vast majority of miscarriages are due to abnormalities in the number of chromosomes contained in the embryo. Many of these are currently detectable by PGD.
Previous failed IVF
Some patients may be predisposed to chromosome errors in their embryos and therefore may benefit from PGD to determine these abnormalities.
Family history
By screening the embryos for chromosomal abnormalities, it is possible to only transfer chromosomally normal embryos during an IVF cycle.
Advanced maternal age
In women aged 35 and older, about 35% of pregnancies are miscarried. Aneuploidy accounts for more than 50% of these losses. With PGD, only chromosomally normal embryos are transferred.
Patients who are carriers of single gene mutations can avoid transmitting those disorders to their offspring by testing the embryos and choosing not to transfer those which are affected or carriers.
Risks and Potential Benefits of PGD
It is important to be aware of both the risks and benefits before commencing with the PGD procedure. We like to keep our patients informed and educated before embarking on this journey.
Benefits of PGD
Reduced incidence of miscarriage
In women aged 35 and older, about 35% of pregnancies are miscarried. Aneuploidy accounts for 50% or more of these losses. By transferring only chromosomally normal embryos, the number of pregnancies going to term should increase. Recent studies have detected a significant reduction in pregnancy losses after PGD, from 23% to 9%. PGD may increase the implantation rate and decrease early miscarriages.
Improved IVF rates
By prioritising chromosomally “normal” embryos for transfer. It is important to understand that PGD is merely a technique to improve the chances of selecting a normal embryo and cannot change the fact that abnormal embryos exist. The pregnancy rate per started cycle is therefore not increased.
Reduced number of embryo transfers necessary
Less embryo transfers may be necessary to achieve a successful outcome because the healthy selected embryo may be selected earlier in the process.
Reduced risk of twin-pregnancy
Less embryo transfers may be necessary to achieve a successful outcome because the healthy selected embryo may be selected earlier in the process.
Potential risks of PGD
Damaged embryos
An embryo is damaged by the biopsy, may not be suitable for transfer into the uterus. During the biopsy the risk of damaging an embryo is less than 1%.
Some biopsied cells may not yield a test result
This is due to degraded DNA which cannot be amplified or loss of cells during transfer to the test tube for CGH analysis. The overall risk is less than 2% per cycle.
Clinical misdiagnosis
The risk of a clinical misdiagnosis resulting in a fetus or baby with chromosomal abnormalities is less than 2%. Due to the low risk of misdiagnosis, prenatal testing by CVS/NIPT or amniocentesis is strongly recommended.
Freezing all embryos due to delayed transfer
All embryos need to be frozen as the transfer will be delayed. This is because the tests need to be conducted on the embryos.
PGS increases the total cost of the procedure
Adding PGS to an IVF program increases the total cost of the procedure and it’s a good idea to weigh this against the potential benefit.
The Process
The embryos used in the PGD process are usually created during the IVF process. The embryos are cultured to the blastocyst stage and a trophectoderm cells biopsy is performed. These cells are then tested for chromosomal abnormalities.
Follicle development and extraction
The process begins the same way as the normal IVF process starts to stimulate follicle growth, whereafter the eggs are extracted and then fertilised with the partner or donor sperm. Read more about the IVF process.
Embryo biopsy
After the embryo has been created it is then cultured for three to five days. Thereafter cells are removed and are tested for chromosomal abnormalities.
Embryo freezing
All embryos are frozen, however, only normal embryos are transferred during a later cycle.
Embryo transfer
Chormosomally normal embryos can be transferred to the uterus using a fine plastic tube. This procedure takes only a few minutes and is usually not uncomfortable. The remaining embryos can also be frozen for a later cycle.
