NEW AND EXCITING DEVELOPMENTS IN IVF PROCESS
Preimplantation genetic diagnosis is one of the most important developments in reproductive technology, helping identify genetic defects within embryos and prevent certain diseases or disorders from being passed on to the child.
What is PGD (Preimplantation Genetic Diagnosis)?
Major improvements in the pre-implantation genetic testing technologies have been developed in the last decade. Preimplantation genetic testing is the sophisticated process of removing a cell from an in vitro fertilization embryo for genetic testing before transferring the embryo to the uterus.
Thanks to PGD, we can prevent serious heritable genetic diseases, thereby eliminating the dilemma of pregnancy termination following unfavorable prenatal diagnosis.
When and how is PDG performed?
Preimplantation genetic diagnosis (PGD) is recommended to couples going through IVF cycles—specifically to couples using the intracytoplasmic sperm injection (ICSI) process—to eliminate the risk of transmitting a known genetic abnormality to their children. Only healthy and normal embryos are transferred into the mother’s uterus, thus diminishing the risk of inheriting a genetic abnormality and late pregnancy termination. During the in vitro fertilization, more than one eggs are collected surgically after ovarian stimulation and the triggering of ovulation. Preimplantation genetic diagnosis or the genetic testing of the embryo can be done at the cleavage (growing) stage, where one to two cells (from the 6-10 cells of the embryo) may be removed from the embryo without detriment. The cells are then sent to a special laboratory that will test for specific genetic diseases and chromosome abnormalities using the most advanced techniques. PGD testing is able to detect the most common chromosome abnormalities, including Down syndrome, Trisomy 18, Trisomy 13, cystic fibrosis, thalassemia, sickle cell disease, and sex chromosome anomalies, in order to reduce the risk of having an affected pregnancy or child.
To eliminate the errors that are rarely observed during PGD examination, a method known as Comparative Genomic Hybridization (CGH) was developed, allowing for the evaluation of every chromosome in a cell by comparing it to other, healthy chromosomes. CGH can be performed at a later stage, 5-6 days after fertilization (at the blastocyst stage), although it is not generally advisable; this particular technique has been shown in several studies to be detrimental to embryo development. The first report of preimplantation genetic testing in humans with a pregnancy resulting was published in 1990, while in Greece the procedure takes place for almost a decade now, at specialized clinics. The potential risks concern mainly the status of the embryo after the PGD examination. According, however, to the European statistics (ESHRE), in 97% of the cases, the removal of cells did not harm the foetus and there is no evidence of birth of abnormal children as a result of embryo biopsy.
PGD can also help determine the gender of the embryo (although not specific characteristics such as eye and hair color, IQ, etc.). Nowadays, science allows gender selection, and one can be 99% sure that the results of the embryo biopsy will represent the ultimate genetics of the foetus and subsequent baby.
However, we should state that according to paragraph 26 of Law 3305/2005, gender selection is only allowed for serious medical conditions. Such conditions include couples that one of them has a chromosomal arrangement called a balanced translocation. When the chromosomes in their sperm or eggs join with those of their partner in the fertilized embryo, they have a high percentage of children with chromosomal abnormalities. This is another situation where PGS can help. Although, gender selection for social reasons (e.g. for family balancing) is illegal, it should not be considered unethical. While many have considered stem cells to be the next frontier of modern medicine, reproductive technology may offer hope to many individuals suffering with rare and unique genetic diseases. PGD can, therefore, also be used for “savior siblings”, to create, in other words, a sibling for the purpose of providing biological material (bone marrow, blood, etc.) that can help treat or cure an existing terminally ill child. While there are banks of tissues and cells and records of potential donors, sometimes doctors can’t treat a patient because they can’t find a suitable match.
The people most likely to have an identical tissue type to the patient are their brothers and sisters, hence the term “savior sibling”. Multiple embryos are created and preimplantation genetic diagnosis is used to detect and select the ones that are free of a genetic disorder and that are also a HLA match for an existing sibling who requires a transplant. Upon birth, stem cells are harvested from the child’s umbilical cord to aid the other child. Thee baby is in no way harmed.