Preimplantation Genetics Diagnosis (PGD) is the medical term for a procedure that takes place before an embryo is placed into the mother’s body. In basic terms, PGD is the process of screening the embryo for the possibility of certain diseases. This allows the pregnancy to continue without the fear that it may have to be terminated due to the onset of the disease in question.
The related preimplantation genetic screening (PGS) differs slightly in that the object is not to look for a specific disease or potential health condition. PGS only makes a general search for an embryo that may have a risk of disease. Some medical experts are not comfortable with the word “diagnosis” in this term because it gives the impression that the health condition or disease is actually identified.
In reality, the embryo tested is at such an early stage in development that it is not possible to detect symptoms. What PGD searches for is a potential condition based on genetics of the family, for example.
Medical history shows that the process has its roots in the late 1960s, when two doctors conducted PGD-like procedures on animals with recognized success. But it took another decade or so before the test could be safely and successfully performed with a human embryo. It wasn’t until approximately 1990 that babies were born after PGD procedures were conducted on the embryo prior to implantation. At about this same time, the medical procedure included what is known as PCR, a test that might show if a patient was carrying any condition linked to the X chromosome. This process allowed doctors to determine the sex of the embryo in some cases.
Over the course of about two decades, PGD and related embryo testing has raised some social and religious concerns. Federal laws have been passed in several countries to address concerns about PGD procedures, including if and when they could be used. Strict licensing plans have been established in some countries to control the use of such testing.
According to medical literature there are two key sections of the population for which PGD might be indicated. These include testing for a particular disease or genetically based health condition for parents who might pass on a condition or physical defect that they inherited. Sometimes this is indicated by an abnormal chromosome condition. Proponents of PGD testing emphasize that knowing of these conditions prior to pregnancy can eliminate the need for abortion later.
A second set of conditions calling for PGD would include potential parents who might need to know about the chances for a successful pregnancy, rather than a possible disease or health issue. These tests are sometimes used for older mothers or women with a miscarriage history, for instance. However, some medical experts note that these situations call for PGS (screening) as opposed to PGD (diagnosis).
Doctors and laboratory personnel have started to identify particular diseases and health conditions that can be identified with PGD. These include sickle-cell disease, certain atrophy and dystrophy conditions, as well as cystic fibrosis.