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What is PGD?
Preimplantation genetic diagnosis (PGD) is a medical procedure that allows embryos created through in vitro fertilization to be tested for genetic defects before implantation in the uterus. During a normal IVF procedure, eggs are collected from the ovaries and fertilized with sperm in a lab to create embryos. With PGD, one or two cells are then removed from embryos 3-5 days after fertilization for genetic analysis before they are transferred back into the womb. This testing helps identify embryos unaffected by specific genetic conditions so that only healthy embryos are selected for implantation.
Why is PGD Performed?
PGD is commonly used by couples who have a high risk of transmitting certain genetic disorders to their offspring. Some of the most common reasons for pursuing PGD include:
– Chromosomal Abnormalities: PGD can detect inherited translocations or inversions of chromosomes that increase the risk of miscarriage or birth defects.
– Monogenic Disorders: Single gene disorders like cystic fibrosis, Tay-Sachs disease, sickle cell anemia, and muscular dystrophy can be diagnosed with PGD.
– HLA Matching: In rare cases, PGD may be used to select an embryo with a tissue type match to an existing child in need of a transplant.
– Family Balancing: In certain situations, PGD allows parents to select embryos of a particular sex for family balancing purposes when a sex-linked disorder is present.
– Aneuploidy Screening: Screening embryos can identify those unaffected by chromosomal defects like an extra or missing chromosome that often lead to miscarriage.
How is PGD Performed?
The basic steps involved in PGD are:
1) Stimulation and Egg Retrieval: As part of a standard IVF cycle, a woman takes fertility drugs to stimulate egg production. Mature eggs are then collected via ultrasound-guided needle aspiration.
2) Fertilization: Eggs are fertilized with sperm in a lab dish to create embryos over a period of 1-6 days.
3) Biopsy: Typically on day 3 or 5 of development, a few cells are gently removed from each embryo using a fine glass needle under a microscope.
4) Testing: The biopsied cells are examined through techniques like fluorescence in situ hybridization (FISH) or next generation sequencing to detect genetic changes.
5) Selection: Only unaffected embryos are selected to be transferred back into the uterus. Typically 1-3 embryos are transferred depending on factors like a woman’s age.
Potential Risks and Limitations of PGD
While PGD can help avoid passing on certain genetic disorders, it does carry several risks, limitations, and ethical concerns:
– Miscarriage Risk: The biopsy procedure can potentially damage embryos, increasing the risk of miscarriage in selected embryos. Reported rates range from 1-5%.
– Diagnostic Errors: Testing may miss or misdiagnose some genetic abnormalities, so a small risk of an affected pregnancy remains. Laboratories must maintain high standards.
– Cost: The costs of IVF, ranging from $12,000 to $17,000 per cycle, are not always covered by insurance. PGD adds $3,000 to $4,000 in testing fees.
– Disposition of Leftover Embryos: Guidelines vary on the fate of any extra embryos detected to have the genetic abnormality or those deemed non-transferrable.
– Slippery Slope Concerns: Some worry PGD could open the door to using genetic data for non-medical sex selection or enhancement. Strict oversight helps minimize risks.
In Summary, preimplantation genetic diagnosis provides an effective way for at-risk couples to conceive a healthy child when performed carefully by experienced practitioners. With appropriate regulations and continued technological advances, more families may benefit from this life-changing technology.
