Preimplantation Diagnosis

What Does PGD Have To Do With Becoming (and staying ) Pregnant?

You may have heard the term PGD. It stands for Preimplantation Genetic Diagnosis, an advanced genetics test used in conjunction with in vitro fertilization to determine the status of an embryo’s chromosomes.

At IVF clinics, physicians are being asked with greater frequency about PGD. It’s easy to understand why: recent studies show that PGD may improve a woman’s chance of a baby being born with a normal number of chromosomes.

How can PGD help improve my chances of becoming pregnant or carrying to term?

Studies reveal that PGD of aneuploidy increases the chance of implantation, reduces pregnancy loss and increases live births. Data suggests a four-fold reduction in the frequency of chromosomally atypical conceptions after PGD.

How does PGD work?

The IVF embryologist carries out the process by removing a cell or blastomere from the embryo on the third day of this development through the use of microsurgical techniques and fixing the cell on a glass slide. Each cell is usually representative of all cells from that particular embryo. Geneticists use a technique called FISH (fluorescence in situ hybridization) to identify the chromosomal makeup of the cell and determine which embryos are most suitable for replacement in the woman’s uterus. In the meantime, during PGD, the embryos develop undisturbed in an incubator.

In some cases polar bodies, two small cells produced by the ripening egg before fertilization, may be tested. This only provides genetic information from the egg. It will not detect abnormalities that may occur after the egg is fertilized by sperm.

Is PGD 100% accurate?

PGD, the only test available to determine aneuploidy, has an accuracy rate of over 90%. There is a false positive error rate of only 4.7%. Yet to identify a false negative (classifying an abnormal embryo as normal), prenatal testing is still recommended via chorioric villous samples (CVS) or amniocentesis.

Are there risks to the embryo?

PGD apparently has no affect on normal development of the embryo or fetus. It is estimated that the removal of one cell reduces the ability of the embryo to implant by less than 3%.

Which patients stand to benefit from PGD?

Virtually all couples over 35 without a history of repeated IVF failures are excellent candidates. Studies show that women who have Recurrent Pregnancy Loss, previous aneuploid conceptions, known chromosome abnormalities and single gene defects, can also benefit. It is not yet clear if women with repeated IVF failures would be good candidates for the procedure. In any of these problems, men as well as women may be the cause of the failure.

What is the cost for PGD?

There is an additional cost for PGD, above that of your IVF cyde. In addition to the removal of the cells from the embryo, a procedure performed at the IVF center, actual testing is done at a specialized laboratory.

If I am interested in PGD, how should I proceed?

Speak to your IVF physician and we'll be happy to assist you.

What should I know about chromosomes?

If you look at a cell under a microscope, you’ll see string-like structures in the cell’s center, or nucleus. These are chromosomes which contain DNA- our genetic roadmap. Normal human cells (for adults, babies, fetuses and embryos) contain 46 chromosomes in 23 pairs, half from each parent.

The condition of having an embryo or zygote with either more or less than 46 chromosomes is called aneuploidy. Very often, the likelihood of aneuploidy increases with the age of the woman, but it can also occur in women under 35. Aneuploid embryos may have extra (called trisomy) or missing (monosomy) chromosomes. A baby carrying an extra or missing chromosome may be born with mental and/ or physical defects. Down syndrome is a common example.

How does aneuploidy affect my ability to conceive or maintain a pregnancy?

A chromosomal abnormality can prevent the embryo from attaching to the wall of the uterus, eliminating any chance of pregnancy. It may also cause the implanted embryo to stop developing, resulting in a pregnancy loss.

More than 50% of embryos from women who are 35 to 39 show chromosomal abnormalities, while those over 40 have a frequency of aneuploidy of 80% or higher. That’s why the percentage of older women becoming pregnant is so low.

Additionally, experts consider aneuploidy to be the biggest factor for Reccurent Pregnancy Loss (of miscarriages) among women 35 and older, responsible at least half the time.

Why is aneuploidy more likely to affect older women?

Since women have eggs that are as old as they are – females have all of their eggs from the fetal stage onwards ; they don’t add new ones later on – experts believe that these older eggs are less likely to divide properly.

Single gene disorders

The term single gene disorder refers to any one of the hundreds of inherited diseases caused by mutation (change) in a single gene.

Common exmples include cystic fibrosis, alpha and beta-thalassemia, myotonic dystrophy, sickle cell anemia, Duchenne muscular dystrophy and fragile x syndrome.

PGD for single gene disorders avoids pregnancy termination.

Preimplantation Genetic Diagnosis (PGD) is now available for virtually all single gene disorders. The aim of PGD is to provide patients at risk of transmitting an inhetited disorder to their children the chance to initiate an unaffected pregnancy. PGD dramatically reduces the likelihood that an affected fetus will be detected during prenatal testing and therefore decreases the probability that parents will face the difficult decision of whether or not to terminate a pregnancy.

The single gene PGD service

The single gene PGD program has proven extremely popular with the number of referrals more than doubling in each of the past three years. The methods used are at the cutting edge of genetic diagnosis, yielding highly accurate results extremely rapidly. Embio single gene tests generally have assay accuracy rates of 99% or higher, with results available within 24 hours of sample receipt (range 5-36 hours).

Unique tests

Every single gene test performed by our designed specifically for the couple requesting PGD. Each protocol takes into account the unique genetic makeup of each individual allowing the production of more reliable tests.

In effect, we have the capacity to develop PGD tests for any single gene disorder. PGD tests for single gene disorders are designed specifically for the couple requesting PGD and therefore extensive preliminary preparation is required . In Vitro Ferilization cycles should not be initiated until the case is reviewed, approved information regarding specific preparation time.

We offer HLA-typing

In addition to PGD for single gene disorders, we have the ability to perform human leukocyte antigen (HLA)- typing of embryos.

There has been a growing interest in HLA- typing of embryos as it allows parents to conceive a child that is capable of providing histocomlatible stem cells in order to save a life of a sibling with a disease. The stem cells are obtained from umbilical cord blood at the time of birth and then trasferred to the affected sibling. This approach haw been used to cure children with a variety of forms of inherited anemia and also for children with leukemia.

Key features of the gene PGD service

• PGD can help parents avoid having to contemplate pregnancy termination
• Available for virtually all single gene disorders
• Diagnostic protocols tailored to individual patients
• Extremely high assay accuracy rates
• Employs analysis of hypervariable polymorphisms for accurate detection of contamination
• Rapid results
• HLA – typing available

Innovation and new services

At our unit we continually strive to extend the services offered to our clients. We will be offering novel technologies in the near future.

What exactly is PGD?

PGD is an advanced genetics test used with in vitro fertilization to determine the status of an embryo’s chromosomes. A normal cell has 46 chromosomes in 23 pairs, half from each parent.

By taking a cell has an extra or missing chromosome. This condition can cause a child to be born with mental and/ or physical shortcomings, such as Down Syndrome.

A chromosome abnormality can also prevent the embryo from attaching to the wall of the uterus, preventing any chance of pregnancy. Or, in the case of many women experiencing Recurrent Pregnancy Loss, it can cause the embryo to stop developing, causing the fetus to spontaneously miscarry.

How likely is it that i may be affected by a chromosome abnormality?

The older you are, the greater the chance that your eggs will be affected. More than 50% of embryos from women who are 35 to 39 have chromosomal abnormalities. For those over 40, the percentages increase to 80% or higher. That’s why older women have far lower pregnancy rates and higher rates of miscarriage. In addition, patients with Reccurent Pregnancy Loss are believed to produce more chromosomally abnormal embryos regardless of age.

How would PGD improve my chances?

Studies have shown that PGD can double the chance of implantation of the embryo, reduce pregnancy loss as much as three-fold, and increase the likelihood of live births. Data even found a reduction in miscarriage among IVF patients who did not have recurrent miscarriage, from 23% to9%. In women with an average age of 40, they found that the chance of an embryo to succesfully impant doubled.

Am I a candidate for PGD?

Women with Recurrent Pregnancy Loss, as well as those who have had problems becoming pregnant, are considered good candidates for PGD.

How and when is PGD performed?

PGD can only be done as part of the in vitro process- at a time when the IVF physician has removed the egg from the female and it has become fertilized with the male’s sperm, prior to being replaced in the uterus.

With PGD, a cell is removed from the embryo through the use of microsurgical techniques and the cell is fixed to a glass slide.

Genetics at our laboratory then examine the cell under a high- powered microscope using a technique called FISH (fluorescence in situ hybridization) to determine the chromosomal makeup. The embryo, meanwhile, remains in a incubator with virtually no risk to its development.

If I am interested in PGD, how should I proceed?

Speak to your physician or;

Contact us with complete discretion about your Preimplantation Diagnosis!

Dr Thanos Paraschos,
trained by the Father of PGD,
Lord Professor Robert Winston