09 April 2015

The 21st March marks the celebration of World Down Syndrome Day. There is no greater blessing on this earth than to be a parent. But sadly some couples carry a gene disorder which can prevent them from carrying a healthy pregnancy. Others may be carriers of specific inherited disorders. Embryo testing allows couples to select the healthiest and most viable embryos for transfer and has enabled many couples to have their own biological children where it was otherwise impossible.

How Does It Work?

Studies have shown that as many as 50% of embryos are chromosomally abnormal and if transferred such embryos are likely to fail to implant in the uterus or may result in a miscarriage. Embryos have traditionally been chosen according to their appearance under the microscope after 3 or 5 days of development in the incubator.  High-tech methods now allow us to perform embryo screening for genetic and chromosomal information.
New techniques of embryo analysis can indicate the chromosomal status of each embryo. This allows us to select high grade embryos for transfer thus reducing the risk of pregnancy failure and improving the chances of having a healthy baby. These advanced techniques of genetic analysis make it possible to screen eggs and embryos for specific abnormalities. The most common embryo testing techniques are preimplantation genetic diagnosis (PGD) and preimplantation genetic screening (PGS).

What is Preimplantation Genetic Diagnosis (PGD)?

PGD is a screening process that enables us to test the embryos of a couple who carry a known genetic marker for a specific inherited disorder so that only healthy embryos are selected to be transferred to the woman’s uterus in order to attempt to achieve a pregnancy. PGD is of great benefit to women with a history of miscarriage, failed IVF cycles and in those of an older maternal age.
Previously, couples carrying the risk for transmitting genetic disorders were only able to diagnose the health of their unborn child after conception had occurred by amniocentesis. Subsequently, if the pregnancy is affected with the abnormality, couples are faced with the dilemma of having to decide whether they would terminate or continue with the pregnancy. For couples who carry the known risk for a serious inherited disorder, PGD offers an alternative to prenatal testing and pregnancy termination.

What is Preimplantation Genetic Screening (PGS)?
PGS generally refers to the screening of chromosomes for aneuploidy (an abnormal number of chromosomes). PGS is the term used more often by fertility specialists when discussing infertility with couples struggling with issues involving age, repeated IVF failures, recurring miscarriages, or having had pregnancies that were genetically abnormal. At Medfem we use PGS to refer to the detection of chromosomally abnormal embryos. This avoids having abnormal embryos transferred to the womb during IVF.
The most commonly known technique for PGS is Array comparative genomic hybridization (aCGH), which analyses a cell from the developing embryo for the correct number of chromosomes. This test can be useful as a screening method for chromosome syndromes and other chromosomal structural changes such as translocations. 

What is the difference between PGD and 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).  

Who can benefit from PGD and PGS?
Possible candidates include:

  • Women aged 35 and over
  • Carriers of sex-linked genetic disorders
  • Carriers of single gene defects
  • Those with a family history of chromosomal disorders
  • Women experiencing recurring pregnancy loss associated with chromosomal concerns
  • Those who have had several unsuccessful cycles of IVF where embryos have been transferred

Benefits or advantages of PGD and PGS:

  • PGD enables couples to pursue biological children who might not have been able to do so otherwise.
  • Performing PGD prior to implantation can reduce the need for amniocentesis later in pregnancy.
  • PGD helps reduce the chance of conceiving a child with a genetic factor. However, it cannot completely eliminate this risk. In some cases, further testing may be required during pregnancy.

For more information on embryo testing visit www.medfem.co.za/embryo-testing


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