Preimplantation genetic diagnosis

Preimplantation genetic checking out is a way used to discover genetic defects in embryos created thru in vitro fertilization (IVF) earlier than being pregnant.

Preimplantation genetic diagnosis (PGD)

Preimplantation genetic diagnosis (PGD) is a procedure designed to examine the embryos that are to be implanted through in vitro fertilisation (IVF) for chromosomal abnormalities or certain hereditary genetic conditions, prior to transfer and implantation. This is done by removing one or two blastomeres from the embryo and testing them. If the embryo is judged to be free of the disorder, they are transferred to the uterine cavity for normal pregnancy.

Preimplantation genetic diagnosis refers specifically to when one or both genetic parents have a known genetic abnormality and testing is performed on an embryo to determine if it also carries that specific genetic abnormality. Without PGD, embryos are chosen only based on their visual quality and morphology, which cannot distinguish chromosomally normal embryos from abnormal embryos. But PGD aims at improving pregnancy and live birth rates by screening embryos for chromosomal abnormalities.

Some of the most common reasons for PGD are specific single-gene conditions such as cystic fibrosis or sickle cell anaemia, and structural changes of a parent's chromosomes. PGD is available for almost any inherited condition for which the exact mutation is known and a unique test must be developed for each couple. The first PGD baby was born in 1992. Since then, successful PGD testing has resulted in the births of more than 7,000 healthy babies.

How is it done?

The PGD process begins with egg retrieval and embryo culture as part of IVF. Once the retrieved egg has been fertilised in the laboratory, the embryo is formed and allowed to develop for five days. One or two blastomeres are removed from the embryo and taken for genetic abnormality testing and analysis. Blastomere biopsy is done at the 6-8 cell embryo stage.

During this time, the embryo is either frozen so that its development is paused, or it is kept in a culture media for further development while the PGD testing takes place. Once the result comes, the embryos which are free of genetic disease are transferred to the uterus. If the embryo is frozen, a frozen embryo transfer is done and normal embryos are transferred to the uterus.

Benefits of PGD

The ability to diagnose and exclude embryos with verified genetic abnormalities prior to implantation and actual initiation of a pregnancy offers at-risk patients a way to prevent passing on inheritable genetic diseases to their children. PGD offers an alternative for couples with single-cell gene defects who would otherwise depend on prenatal diagnosis to determine the genetic status of their pregnancy. In addition, since only genetically normal embryos are transferred to the uterus, many couples have been able to avoid clinical pregnancy termination later on.