Pre Implantation Genetic Diagnosis (PGD) for IVF Success

Embryo selection is more important than ever in successful in vitro fertilisation or IVF treatment, because these days fewer embryos are being placed into the uterus during IVF treatment.

To improve the chances of success of an IVF cycle and to prevent chromosomally abnormal embryos being transferred during IVF, pre implantation genetic diagnosis (PGD) is used for the testing of early stage embryos (up to 5 days old) for genetic abnormalities.

During in vitro fertilisation or IVF treatment, an egg cell is fertilised with sperm outside of the body in a lab (‘in vitro’ literally means ‘in glass’) to form an embryo. The fertilised egg or embryo is kept safe in an incubator for a few days before being transferred to the uterus to hopefully implant and become a pregnancy.

Studies have shown that as many as 50% of fertilised eggs or embryos are chromosomally abnormal. If transferred into the uterus during IVF treatment, these chromosomally abnormal embryos are likely to fail to implant in the uterus or may result in a miscarriage.

Traditionally, embryos have been chosen for implantation according to their appearance under the microscope after 3 or 5 days of development in the incubator. This meant that couples carrying the risk for transmitting genetic disorders were only able to diagnose the health of their unborn child after conception. As a result, if the pregnancy was affected with a genetic abnormality, couples were faced with the dilemma of having to decide whether they would terminate or continue with the pregnancy.

High-tech methods now allow us to perform embryo screening for genetic and chromosomal information. These new techniques of embryo genetic analysis can indicate the chromosomal status of each embryo, making it possible to screen eggs and embryos for specific abnormalities. This allows our fertility specialists to select high grade embryos for transfer, thereby reducing the risk of pregnancy failure and improving the chances of having a healthy baby.

The most common embryo testing techniques are pre implantation genetic diagnosis (PGD) and pre implantation genetic screening (PGS). PGD involves detection of single gene disorders and PGS involves the detection of chromosomally abnormal embryos that result in IVF failure, miscarriages or babies born with Down’s syndrome (Trisomy 21) or Edward’s Syndrome (Trisomy 18). The term “pre implantation” is used because testing is performed on embryos during the time before they implant into the uterus.

PGD is a screening process used to identify certain chromosomal abnormalities in embryos. It enables the embryos of a couple who carry a known genetic marker for a specific inherited disorder to be tested, so that only healthy embryos are selected to be replaced/transferred to the woman’s uterus during IVF.

PGD testing has been used for more than 20 years and is very successful in detecting genetic alterations in the embryos of couples known to be at risk of passing on an inherited disease to their children. It offers an alternative to prenatal testing and pregnancy termination, by screening embryos (fertilised eggs) before pregnancy is established. Amongst infertile couples, PGD testing also enables the identification of chromosomally normal embryos for transfer which improves IVF pregnancy rates. As such, PGD is of great benefit to women with a history of miscarriage, failed IVF cycles and in those of an older maternal age. It is routinely used for patients older than 37 years of age and patients with several unsuccessful cycles of IVF and/or recurrent miscarriages associated with chromosomal concerns, as well as to identify the gender of the embryo.

Any couple at risk for passing on a genetic disease or condition can benefit from pre implantation genetic diagnosis and screening. Possible candidates include women aged 35 and over; carriers of sex-linked genetic disorders; carriers of single gene defects; and those with a family history of one of several hundred known single gene or chromosomal disorders, such as Cystic fibrosis, Hemophilia, Huntington’s Disease, Hypertrophic Cardiomyopathy, Marfan’s Disease, Muscular Dystrophy, Robertsonian Translocations, Sickle Cell Anemia, Spinal Muscular Atrophy, Tay Sachs, and Thalassemia.

In this video, you can see how PGD is done at Medfem Fertility Clinic in Sandton, Johannesburg. At Medfem Fertility Clinic, five different probes and therefore five different chromosomes are tested during PGD. These chromosomes are Chromosome X, Chromosome Y, as well as Chromosomes 13, 18, and 21.

During pre implantation genetic diagnosis a single cell is isolated from a day-three embryo without damage to the embryo, so the embryo goes back into culture, and stays safe and sound in the incubator, while the single cell undergoes further testing.

With the help of a micro manipulator, a very sophisticated machine, and under an inverted high-powered microscope, the embryo is stablised, before a little hole is made in the capsule of the embryo with a very tiny micro glass pipette. Biopsied cells are sent for testing (PCR, CGH) or analysed using a procedure called Fluorescent In Situ Hybridization (FISH). The single cell is placed in a specialised medium and the DNA is denatured, hybridised and stained with fluorescent dye which allows our embryologists to identify the different chromosomes by using a series of markers or colours under the fluorescent microscope.

For example, in the video, the X chromosome has a purple colour and the Y chromosome a golden colour, while chromosome 13 has a red colour and 21 a green colour. So, looking at a single cell under the fluorescent microscope, there should be in normal circumstances either two purple X signals for a female embryo, or an X and a Y which is the purple signal and the golden colour signals, which will indicate a male embryo. Two of each of the other chromosomes (13, 18 and 21) will indicate a normal embryo – but if there are three or more of a certain chromosome, or just one, it will raise red flags.

Although the embryo could be chromosomally normal for those chromosomes being tested, at Medfem Fertility Clinic we also look at the development of the embryo, as well as the morphological status of the embryo. The most important thing is that the embryo should be able to develop and progress and grow if implanted in the uterus.

To ensure our patients have the best chance of a successful IVF treatment, only embryos that are good quality blastocysts are transferred to the uterus on day five or even day six.

By offering our patients PGD, our team at Medfem ensures that couples who might not have been able to do so otherwise, can pursue their dream of having their own biological children. PGD helps reduce the chance of conceiving a child with a genetic factor. However, in some cases, further testing done during pregnancy is needed to ascertain if a genetic factor is still possible. But, because PGD is done prior to implantation, the need for amniocentesis later in pregnancy can be reduced.

At Medfem Fertility Clinic, we believe in making world-class fertility treatments available for everyone. PGD is just one of the ways in which our team at Medfem ensure that our pregnancy rates are among the highest in the nation. A leader in fertility care, Medfem performs an average of 1,100 IVF treatment cycles a year – and is proud to have played a role in bringing more than 16,000 babies into the world.

It is our joy and commitment to give you a positive outcome to your fertility journey, so you will have a fond memory of feeling empathy, caring and being part of the Medfem Fertility Clinic family.

If you would like to meet one of our fertility specialists at Medfem Fertility Clinic, simply click here to book an initial consultation or contact us telephonically on +27 (11) 463 2244.

We look forward to meeting you!

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