PGD (Preimplantation Genetic Diagnosis )
PGS (Preimplantation Genetic Screening )
PGD is a reproductive option for couples at risk of passing a specific genetic disease or chromosome imbalance to their children. PGD involves screening IVF generated embryos for genetic conditions prior to embryo transfer, with only unaffected embryos transferred to the uterus. This provides the opportunity to screen embryos for genetic conditions before a pregnancy is established.
Couples choose PGD over prenatal diagnosis ( identifiying the abnormalities of the baby during pregnancy period ) for many reasons including objection to termination of pregnancy, loss of a child from the genetic disease, recurrent implantation failure or recurrent miscarriage.
PGD testing may be appropriate for:
Couples at risk of passing a single gene disorder on to their children
Couples at risk of having children with a particular X-linked disorder
Couples where one partner carries a balanced chromosomal translocation
PGS ( Premiplantation Genetic Screening ) may be appropriate for:
- Couples with advanced maternal age (>39)
- Couples who have experienced repeated miscarriage
- Couples who have experienced repeated IVF failure
- Couples who have previously had a pregnancy with a chromosomally abnormal child
Genetic counselling is an important step to ensure that PGD is the right option for each couple.
What does PGD/PGS involve?
All couples requesting PGD/PGS should first undergo an IVF cycle to stimulate their ovaries to produce a number of eggs. These eggs are collected and fertilised using the male partner’s sperm. The resulting embryos are cultured in the laboratory. Embryo biopsy can be performed either on Day 3 or Day 5 after egg collection. Embryos that have developed to at least 5-6 cells are suitable for biopsy. A hole is drilled in the outer shell of the embryo using laser and 1 or 2 cells are removed for genetic analysis. This procedure which is done at the 3rd day gives us the chance of having fresh transfer on the 4th or 5th day. The embryos are kept in culture while the testing of the biopsied cells proceeds. Genetic test results are usually obtained within 24 hours of embryo biopsy. Our embryologists will discuss the PGD results with the couple at the completion of testing. When available, one or two unaffected embryos can be transferred on Day 4 or Day 5. As a number of embryos are identified as being genetically suitable for transfer, morphological criteria are used to determine the best embryo/s for transfer. Surplus unaffected embryos will be grown in culture to Day 5 or Day 6. If they reach an appropriate stage of development (ie: form a good quality blastocyst) they will be frozen. These embryos may be used in a subsequent IVF cycle if the couple do not achieve a pregnancy with the fresh embryo/s. Embryos that are affected or have a chromosome abnormality are discarded.
For the last two years, we prefer performing PGS (Preimplantation Genetic Screening ) procedures ( not targeting a specific disease ) at the 5th day instead of the 3rd day. We wait until the 5th day after the egg collection to choose the best ones and take the embryo biopsy from the trophectoderm cells instead of the embryo itself. So, the theoretical risk of damaging the embryo becomes virtually zero and the number of the embryos to be screened decreases causing a lower cost. We use NG-CGH (Next Generation Comparative Genomic Hybridization ) technology to check all ( 24 pair ) the chromosomes of the embryos for screening purposes such as advanced maternal age or repeated implantation failures.
A debatable disadvantage about this procedure ( Day 5 biopsy ) is that we should freeze the embryos since the results will be available in 24 to 36 hours which can be too late for the fresh transfer. The only issue is that couples come to our centre again in two months ( or whenever they wish complete the cycle..) for only a few days for the transfer of the healthy embryos found. Our statistics show that the pregnancy rates are exactly the same as the fresh ones. Furthermore, some recent studies reveals that transferring the frozen embryos may give even higher implantation rates since ovarian stimulation with high dosage of hormones may impair the endometrial receptivity. It is very easy to have frozen embryo transfer and there is no need to use any injections.
If all embryos to have some kind of chromosomal abnormalities, transfer is cancelled. But we believe that this is much better than realising the baby is not healthy during the pregnancy with a probable miscarriage or with an affected child such as down syndrome…
Please fill our inquiry form to have more information about our IVF + PGS/PGD procedures and related costs.