The advent of preimplantation genetic diagnosis (PGD) makes it possible for couples that have a genetically transferable disease to virtually eliminate the possibility of passing it to their child. For example, a woman with hemophilia has a very high probably of passing the disease to a male child. To prevent this transference, only female embryos identified using PGD will be transferred.

PGD can identify an abnormal number of chromosomes (aneuploidy), or broken or translocated chromosomes. 

PGD is performed on embryos after fertilization and culture in an IVF cycle. Once the embryo reaches the six to eight cell stage, one cell is removed for PGD examination. The removal of the cell does not harm the developing embryo.

Two types of procedures are performed using PGD: the polymerase chain reaction (PCR) and the fluorescent in situ hybridization (FISH) procedure.

PCR is used to screen for single gene defects such as Down syndrome, Turners’ syndrome and cystic fibrosis. Multiple copies of the suspected area of the chromosome are copied.  When a parent has a genetic disease, a probe based on his or her chromosome abnormality can be used to identify the genetic disease in the offspring. When an embryo is found to have the genetic disease, the embryo is not transferred to the mother.

FISH is a procedure that involves staining the chromosomes with various dyes that become visible under fluorescent light. For example, the male and female chromosomes stain different colors, allowing gender selection. FISH can also identify broken or translocated chromosomes, or if the number is chromosomes is abnormal.

PGD is used when a genetic disease is suspected, in older women where the miscarriage rate is higher, after multiple failed IVF attempts, for gender selection, or when deemed appropriate by the physician and couple.