Preimplantation Genetic Diagnosis

What is Preimplantation genetic diagnosis, PGD?

Preimplantation genetic diagnosis is a technique used in conjunction with IVF where embryos can be screened for genetic diseases or specific heritable chromosomal disorders. Embryos are screened before they are implanted back into the uterus, so that abnormal embryos can be identified. Only embryos that can result in a normal child are transferred into the uterus.

How is PGD different from Preimplantation genetic screening, PGS?

PGD is a technique where embryos can be screened for genetic diseases or specific heritable chromosomal disorders whereas PGS is a technique used to screen for chromosomal abnormalities that occur as a result of aging.

Who should undergo PGD?

PGD is recommended for the following patients

• One or both partners are carriers of an heritable genetic disease
• One or both partners are carriers of a specific chromosomal abnormality

Heritable genetic disorders

Heritable genetic disorders are typically caused by a mutation in the genome. Examples of heritable genetic disorders are Cystic Fibrosis, Thalasemia, and Spinal Muscular Atrophy. If the mutation that causes the disease has been identified then embryos created through IVF can be tested to look for that specific gene mutation. Therefore, PGD can be used to screen the embryos to determine if the embryos have the disease, are carriers for the disease or are unaffected.

By determining which embryos contain the gene mutation, couples can make informed decisions about selecting which embryos to transfer back into the uterus. The ability to select a healthy embryo for transfer will greatly decrease the chance that the child will be affected by the disease. The timing of the process is critical, in that embryos are tested before implantation, therefore before a pregnancy is even established, eliminating the potential of having to contemplate termination of a pregnancy.

PGD is useful in the following situations.

  • Couples who already have/had a child with a heritable genetic disease
  • Couples who have had a pregnancy loss as a result of a heritable genetic disease
  • Couples who have family members who have a known heritable genetic disease
  • Couples who find out that one or both partners are carriers of a heritable disease during preconception genetic screening

The process to develop testing for a specific gene mutation is a detailed and individualized process. In many cases, genetic companies may have to develop a specific test solely to test for your gene mutation. Therefore, the cost and time involved will vary depending on which gene mutation is involved.

Chromosomal disorders

Chromosomal disorders are abnormalities that are carried in the parental genome and can be transmitted to the offspring. Examples of these disorders are translocations, inversions and deletions involving any of the chromosomes. Heritable chromosomal abnormalities can result in implantation failure, recurrent miscarriage, pregnancy loss, or babies born with genetic syndromes associated with congenital anomalies or mental retardation. If the chromosomal abnormality has been identified then embryos created through IVF can be screened to determine if the embryos also contain that chromosomal abnormality or another abnormality resulting from the original abnormality.

By determining which embryos contain chromosomal abnormalities, couples can make informed decisions about selecting which embryos to transfer back into the uterus. The ability to select a healthy embryo for transfer will greatly decrease the chance that the child will be affected as a result of a chromosomal abnormality. The timing of the process is critical, in that embryos are tested before implantation, therefore before a pregnancy is even established, eliminating the potential of having to contemplate termination of a pregnancy.

PGD is useful in the following situations:

  • Couples where a partner was found to be a carrier of a chromosomal abnormality
  • Couples with infertility as a result of a chromosomal abnormality
  • Couples having recurrent miscarriages as a result of a chromosomal abnormality
  • Couples with previous pregnancy loss as a result of a chromosomal abnormality
  • Couples who have a child who has medical issues as a result of a chromosomal abnormality
  • Couples with family member was found to be a carrier of a chromosomal abnormality

Should I see a genetic counselor before undergoing preimplantation genetic diagnosis?

All patients who are considering PGD must have a consultation with a genetic counselor to discuss their specific case. Each case involving genetic screening is individual and can be complex. As patients you deserve the time and attention so that you can be thoroughly counseled as to what the potential issues are relating to your specific heritable disease or abnormality and what appropriate testing is available.