Preimplantation Genetic Diagnosis is sophisticated and technologically advanced testing that is used to identify genetic defects in embryos created by means of in vitro fertilization (IVF) and even defects in oocytes before transferring them into the woman?s body. This procedure is especially recommended when embryos may be affected by a certain genetic condition or chromosomal disorder in order to increase the likelihood of an ongoing pregnancy and to prevent an inherited condition being passed on to the child. PGD is also sometimes used for sex selection.
Technically speaking, PGD is a poorly chosen phrase because, in medical terms, to “diagnose” means to identify some illness or to determine its cause. Of course, an oocyte or early-stage embryo has no symptoms of disease. Rather, they may have a genetic condition that could lead to disease. Therefore it is probably more accurate to refer to preimplantation genetic screening because it is being tested for a genetic condition when an absence of disease symptoms is determined.
PGD begins with a standard process of artificial insemination which includes egg retrieval and fertilization in a laboratory. Over the next three days the embryo will divide into 8 cells. In course of PGD a single cell is removed from the embryo using small instruments referred to as pipettes. Then DNA is extracted from this cell and the DNA sequence code is evaluated by molecular analysis to determine if the inheritance of the gene is present.
Once the PGD procedure has been performed and embryos free of genetic problems have been identified, implantation may be attempted through embryo transfer, intracytoplasmic sperm injection (ICSI), or zygote intrafallopian transfer (ZIFT).
Consequently, only healthy and normal embryos are being implanted that greatly reduces the risks for the baby to get specific genetic or chromosomal abnormality as well as minimizes chances of adverse consequences including miscarriages, pregnancy termination or birth defects (physical and/or mental). Nowadays it is possible to test for many different diseases through PGD, including but not limited to aneuploidy, single gene disorders and chromosome translocations.
One of the greatest advantages of PGD is that that the procedure is performed before foetus implantation, allowing the couple to elect whether to continue with the pregnancy or not.
Preimplantation genetic screening may be also of great assistance to the couples endeavouring surrogacy programs, namely allowing the Intended Parents to be sure that oocytes or embryo implanted into the uterus of Surrogate Mother are free of genetic disorders.
Nevertheless it is worthwhile to note that PGD is rather controversial technique and is not offered far and wide. In many countries PGD is prohibited, in others it is controlled by the state.
As for Ukraine, the ?Instruction on Procedures for Assisted Reproductive Technologies?, adopted by the Order of the Ministry of Health of Ukraine No. 771 of 12/23/2008 stipulates that preimplantation genetic screening of oocytes and embryos for monogenic disorders and chromosome abnormality as well as determination of the embryo?s sex preventing an inherited condition related to the child?s sex is developed as an alternative method of prenatal testing for women who are at risk of passing on an inherited genetic decease to their issue.
So Ukrainian medical centres successfully perform preimplantation genetic screening in their practice, which is in particular conducted by means of such micromanipulation techniques as:
-Fluoresecent in situ hybridization (FISH), when a portion of the embryo containing chromosomes is removed, the DNA probe is added and the cell is visualized under a microscope;
– Polymerase chain reaction (PCR), when a single strand of DNA is extracted from a fragile embryo and is ?mass produced? and analyzed.