What PGD Can Do For You
Healthy pregnancies become much more likely if the early embryo can be genetically screened for abnormalities. In vitro fertilization offers an ideal opportunity to conduct such embryo screening. Following fertilization, the zygote naturally cleaves into “blastomeres”. These cells are virtually identical to each other. Genetically testing these blastomeres can usually reflect the genetic integrity of the entire embryo. During PGD, one or two blastomeres are carefully removed from an embryo via micro-manipulation procedures. In this manner; genetic testing can be safely and efficiently conducted prior to the implantation procedure.
Patients Who Need PGD
In rare cases chromosomes can be “chaotic”, and 100% display abnormal characteristics. These individuals are typically infertile.
PGD can also screen embryos for:
Single-Gene Disorders: To rule out cystic fibrosis, Tay-Sachs disease, and sickle cell anemia.
Gender Selection: To rule out gender-related genetic disorders, such as hemophilia and X-chromosome linked mental retardation.
Chromosome Translocation: To rule out inherited chromosome translocation, which may result in severe physical and mental abnormalities.
Two types of biopsy are possible: Blastomere and Polar Body
PGD Procedural Details
An embryo, artificially fertilized for IVF, is laboratory cultured for 3 days. By this time, the embryo is comprised of 6 to 8 blastomeres.
A biopsy is then performed on the embryo with micro-manipulation techniques. Typically, 1 or 2 blastomeres are removed for analysis. At this early stage of embryonic development, the blastomeres have yet to differentiate, and are typically identical to each other in every meaningful way.
Blastomeres are genetically tested using one of two methods: Fluorescence In Situ Hybridization (FISH), or PCR-based DNA amplification. Results can be available within two days. During testing, embryos can be cultured or cryopreserved for future implantation.
Years of successful PGD work in animals and numerous human tests have proven the procedure to be both safe and reliable.
Note that potential problems with FISH technology include hybridization errors, other technical difficulties, and an incapacity to detect structural abnormalities frequently associated with birth defects. Problems with PCR technology include possible amplification complications, and other technical concerns. These may result in a small probability of missing an abnormality, or excluding a normal embryo. The estimated error rate, however, is less than 10%.
In some cases, mosaicism may further complicate the diagnosis. Although irrelevant to blastomere biopsy work, a correlation has been observed between mosaicism as identified by FISH, and that analyzed through karyotyping of amniotic cells. As a precaution, though, all patients who have utilized PGD should also routinely undergo prenatal testing.
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