PRE-IMPLANTATION GENETIC DIAGNOSIS
What is PGD?
Pre-implantation Genetic Diagnosis (PGD) is a technique used in assisted reproduction whereby genetic defects can be identified in embryos before implanting them back to the uterus. To become parents of a healthy and normal baby is a dream of every couple. However, when both or either of the partner has any known genetic abnormality, they fear of it for passing on to their offspring. Basically, PGD embryo testing is a method used to recognize inheritable hereditary illness in the embryos. During PGD, embryos are tested to determine whether they carry any genetic abnormality so, the healthiest embryo can be implanted to the uterus to have a normal and healthy baby delivered.
Does PGD help in Gender Selection?
Besides detecting the transmission of any genetic disorder, PGD also helps in family balancing as it allows the couples to select the gender of the child. Couples, who already have a child of certain gender, are often interested to have their subsequent child of the opposite gender. At Australian Concept Infertility Medical Center, we use a combination of Intracytoplasmic Sperm Injection (ICSI) and Pre-implantation Genetic Diagnosis (PGD) which allows us to identify the gender. The combination of PGD with ICSI is the most accurate approach for determining the gender with about 99% accuracy.
How PGD helps in Family Balancing?
Every couple desires a balanced family, PGD embryo testing is a great choice for such couples to fulfill their wishes. FISH (fluorescent in-situ hybridization) technology is well0accredited and established in infertility clinic all over the world which allows scientists to configure the embryos based on X and Y chromosome prior to implantation. This technique is also used during PGD to determine the gender of an embryo. During FISH technique, two DNA probes are used, each of which identifies X and Y chromosomes. The molecules attached to these probes light in different colors which helps the embryologist determine the gender of an embryo.
How accurate is PGD testing?
Data reveals that PGD is 99% accurate in determining gender at embryonic level of day 3. However, it is to be kept in mind that there is a 1% chance of failure. In addition to this, there is a rare chance that all embryos may be of same gender hence, no scope for selection. As far as genetic abnormalities are concerned, PGD is shows up to 98% accuracy.
Is PGD helpful for the identification of any Genetic Abnormality?
PGD has been proven to be quite helpful in determining any genetic abnormality in embryos. It is basically a technique used to identify any such abnormalities that may be transmitted to the embryo due to assisted reproduction. It is quite helpful when both or either of the partners have any known genetic abnormality which may be passed on to their children. When any or both of the parents have any known genetic abnormality, biopsy is carried out on the embryo to determine whether or not it carries the same. Diseases Diagnosed through PGD
- Sickle cell anemia
- Spinal muscular atrophy
- Tay-Sachs disease
- Fragile X syndrome
- Myotonic dystrophy
- Hemophilia A
- Duchenne muscular dystrophy
- Huntington’s disease
- BRAC 1 & BRAC 2 genetic mutations
Is PGD testing always Successful?
Couples desiring to undergo or those undergoing PGD with ICSI/IVF should always keep in mind that it is not always successful. At Australian Concept IVF Clinics, each couple is counselled about the success rates. Besides, there are a number of factors upon which the success rate is dependent, such as::
- Maternal age
- Ovarian reserve
- Quality of sperm
- Development of embryo
- Embryo survival post biopsy
- Weight
What are the steps in PGD?
Once the initial assessment is completed, the procedure of ovarian stimulation begins. During the day 2 of your menstrual cycle, injections for ovarian stimulation are administered daily at a specific time. At Australian Concept Infertility Medical Center, we have trained nurses for the purpose. This stage lasts for nine to twelve days. The main aim is achieving over 10 matured follicles. During this stage, follicles are monitored through transvaginal scan on alternate days.
When the desired level of estradiol and follicles is achieved, trigger injection is administered. This injection is administered approximately 36 hours prior to egg retrieval.
As mentioned earlier about 36 hours after the trigger shot is administered, the eggs are collected from the ovaries. This procedure is done by experienced specialists in the presence of highly trained team of consultants, embryologists, nurses and anesthetist as it is a very delicate procedure. During this stage, the patient is sedated and eggs are retrieved from the ovaries using an ovum pick needle guided by transvaginal ultrasound. It is a day case which takes about 30 minutes to be completed. Meanwhile, sperm is also collected from the male partner and prepared for fertilization stage.
After the retrieval, sperm is injected in to the cytoplasm of eggs using Intracytoplasmic Sperm Injection (ICSI) technique. Through ICSI, embryologist injects the healthiest sperm into the egg using a specialized glass needle. The procedure takes place under a high-powered microscope.
When the eggs start to grow and develop, the embryologist monitors how many eggs are dividing into further cells. When the cell division reaches to the formation of 6 to 8 cell, biopsy is performed. During biopsy, one or two cells are removed from each embryo with an aim to identify the gender and to determine any potential genetic disorders. The same biopsy can be used for PGS. The genetic report arrives in about fifteen days after which the embryo transfer takes place.
After successful testing, the couple is informed about the genders of the embryos and of any gender disorder (if detected). Afterwards embryo with the desired gender, as selected by the couple, is implanted to the uterus.
After embryo implantation, there are extra embryos left that were not used. Couples are asked whether they want to freeze them for future use or dispose them off. As per their will, the embryos can be frozen as freezing them can help in another attempt in future and the couple will not have to go through all the grind of an IVF cycle again. Even if the attempt is successful, frozen embryos can be used to in case the couple decides to expand their family.
After about two weeks of embryo transfer, a pregnancy test is conducted in order to determine whether or not the treatment has been successful.
Who should consider PGD?
The main goal of PGD is to mitigate the risk of passing down genetic disorders to your offspring. Moreover, it is also useful for couples who desire to have a balanced family as it allows the parents to be to select the gender of their child. While it can be considered by every couple undergoing IVF, it is most beneficial for those who have a potential risk of passing on a known genetic disorder to their offspring. Besides, it can also be considered by:
- Women who have had recurrent miscarriages
- Women above the age of 37 years
- Men with sperm disorders such as, poor motility or morphology, etc
- Couples having a family history of chromosomal abnormalities and genetic mutations
- Couples who desire to match stem cells in case of tissue donation to any family member
- Women with a history of failed infertility treatments i.e., more than one
- Couples who are carriers of sex-linked genetic disorders
- Couple or either partner having history of “known” single-gene disorder i.e., Tay Sachs disease, Cystic fibrosis, etc.
- Women who have experienced a pregnancy with chromosomal abnormality or genetic disorder
- Couple or either partner with chromosomal translocation (chromosome is found at a place other than its normal location)
Risks Associated with PGD
Multiple Pregnancies
This may happen due to the transfer of more than one embryo to the uterus. Multiple pregnancies resultantly increase the risk of complications.
Miscarriage:
However, there is no evidence to support the risk of miscarriage due to PGD but multiple pregnancies may lead to miscarriage. Moreover, the risk of miscarriage is generally present in assisted reproduction.
Damage to Embryo(s):
This may happen due to the transfer of more than one embryo to the uterus. Multiple pregnancies resultantly increase the risk of complications.
False PGD Testing:
It can lead to miscarriage if an abnormal embryo is implanted to the uterus. Besides, the false test might reveal that no embryo is normal enough to be transferred to the uterus. There is chance that PGD might not screen possible embryonic abnormalities and identifies gender falsely. In rare cases, FISH signals of X and Y chromosomes are not detectable.
Side Effects of Drugs
Due to medications following side effects can take place,
- Hot flashes
- Mild bloating
- Stomachache
- Fatigue
- Restlessness
- Nausea / vomiting
- Mood swings
False PGD Testing:
It might take place as a side effect of medications administered for ovarian stimulation. The symptoms of Ovarian Hyper-Stimulation Syndrome include:
- Abdominal pain
- Shortness of breath
- Mineral imbalance
- Pelvic infection
Benefits of PGD
PGD has numerous benefits. Through PGD you can:
- Identify embryos that carry genetic disorders hence, not using them for implantation
- Allow couples with known genetic disorders to implant an embryo which has significantly low risk of passing on the concerned disorder to their child
- Significantly improve the chances of a successful and healthy pregnancy
- Identify and select the gender of your child
Difference between PGD and PGS
While PGD (Pre-implantation Genetic Diagnosis) and PGS (Pre-implantation Genetic Screening) both are conducted prior to embryo implantation, they differ in their essence and purpose. PGD refers to diagnosis of a definitive disease or disorder that is known to be present in both or either of the intended parent. PGS, on the other hand, refers to screening of embryos for genetic defects such as chromosome aneuploidies. PGD aims at the reproduction of a disease free child whereas, PGS aims at improving the outcome of IVF as well as having a normal and healthy child.