Preimplantation genetic diagnosis (PGD) is a procedure whereby individual cells are biopsied from the patient’s embryos before they are transferred back into the uterus. The intention of performing the embryo biopsy is to select against embryos which may be chromosomally or genetically abnormal as well as to improve implantation rates.

Currently accepted indications for PGD include:

• Screening for single gene mutations and X-linked disorders in at-risk couples 
• Screening patients who are carriers of a numerical chromosome abnormality 
• Aneuploidy (having an abnormal number of chromosomes) screening for: 
  • Patients with advanced maternal age
  • Patients with multiple IVF failures 
  • Patients with a history of recurrent spontaneous miscarriage

PGD requires obtaining genetic material from an egg or an embryo. There are two types of biopsies performed. Polar body biopsy enables assessment of the genetic complement of the egg and provides indirect information of the genetic status of the egg in conditions where a genetic disorder is of maternal origin. Blastomere biopsy involves removing one or two cells from an early embryo and provides genetic information of maternal or paternal origin (if either parent is a carrier of a disorder) as well as information specific to that embryo (spontaneous mutations and sex).

Several techniques are employed to identify the genetic abnormalities. Polymerase chain reaction (PCR) is the method used to detect single gene mutations and involves isolation and amplification of short DNA fragments. Common single gene mutations that have been diagnosed with PGD and PCR include but are not limited to Cystic Fibrosis, Beta-Thalassemia, Sickle Cell Anemia, Tay-Sachs disease, Myotonic Dystrophy, Huntington’s Chorea, Fragile X, and Duchenne’s Muscular Dystrophy.

Fluorescent In-Situ Hybridization (FISH) is a technique to determine abnormalities in the chromosomes within a particular blastomere. Fluorescently labeled probes that recognize specific sequences of a specific chromosome are allowed to hybridize to the cell. The cell may then be analyzed under a fluorescent microscope to identify the presence or absence of the particular chromosome(s) in question. This technique is employed to evaluate embryos of patients who are carriers of a numerical chromosomal abnormality as well as for assessment of aneuploidy that occurs more frequently as a result of reproductive aging.