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.

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.

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 (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 fetus and subsequently of the baby.

However, we should state that according to paragraph 26 of Law 3305/2005, gender selection is permitted for strictly medical conditions. Such cases involve, for example, couples with abnormal genes on their sex chromosomes who, if they have children of one sex, will be born healthy, while the other sex will be born abnormal. Thanks to the sex selection facility with the PGD test, we only select embryos of the sex that will give healthy children. However, sex determination, for example in cases where a family just wants to have offspring of both sexes (family balancing), is not allowed.

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.

Another valuable contribution of PGD in medicine has to do with the selection of the genetic characteristics of the embryo to be implanted for the health of a third person (savior sibling). For example, some diseases, such as certain types of leukemia and anemia, require bone marrow transplantation for their treatment. However, bone marrow transplantation requires a donor who is immunologically compatible with the recipient. If no compatible donor is available, it is possible for parents to have another baby who will literally save the sick sibling. With PGD testing, healthy embryos, immunologically compatible with the sick child, are selected for embryo transfer. At birth, blood is collected from the umbilical cord and transplanted into the sick sibling to replace the abnormal bone marrow. The baby is in no danger from the procedure, and children born in this way are known as ‘savior siblings’. However, although we would like to report the percentage of these children, unfortunately there are no statistics available on the number of these children.