Blastomere Biopsy :
- Biopsies done at 6-8 cell stage of embryo a hole is made in the zona with laser just sufficient to delink the blastomere from the developing embryo and gently pulled out and fixed on a slide for genetic study.
- After removal of one blastomere the developing embryo is placed back into culture media and returned to CO2 incubator for further development.
- At this early point of embryo development , all the cells are equivalent and thus, removal of a one blastomere does not remove any thing critical for normal development. The embryo compensates for the removed cell and should continue to divide following blastomere biopsy.
- Removed blastomere can be analysed using a technique called PCR or FISH.
- Results are usually obtained by noon on day 5 of embryo development according to the result normal embryo will be transferred to uterine cavity in hope for implantation.
Polar Body Biopsy :
Polar body from the oocyte can be removed and tested for its chromosome complement or to identify whether it contains the abnormal gene of concern. The polar body have no known function except to assist in cell division. They are simply “by-products” of the oocytes division. Once implantation occurs, the polar body disintegrate and are not part of the developing fetus.
In some instances it is necessary to confirm a diagnosis made on polar body analysis by performing blastomere biopsy. It is also possible that polar body fail to provide a conclusive result. In these situations , it may be possible to perform blastomere biopsy for further genetic analysis.
FISH : [Fluorescence Insitu Hybridization]
FISH is used to determine the proper structure of specific chromosome. A probe or “tag” attached to a specific chromosome by matching the sequence of the probe with the sequence of the DNA being tested. The probe has fluorescence and “lights up” under a microscope. Embryos with too much or too little fluorescence have an abnormality. This technique is most useful in diagnosing recurrent miscarriages, repeated IVF failures, age related chromosome abnormalities, abnormalities of chromosome 13,15, 16,17,18,21,22 , X & Y.
PCR [Polymerase Chain Reaction]
PCR is a DNA analysis technique and useful for specific single gene disorders, such as cystic fibrosis or Tay sechs. An enzyme is used to make millions of copies of the cellular DNA. This availability of abundance of the DNA facilitates easy evaluation of specific gene disorders. The sequence of base pairs in DNA helix is compared with normal gene and disorders are identified.
Some embryos may contain blastomeres which are genetically normal, and within the same embryo, other blastomere which are abnormal, is called mosaicism. Misdiagnosis can occur due to mosaicism. This may result in the transfer of an embryo carrying a chromosome abnormality or the failure to transfer a normal embryo.