One of the most powerful tools available in reproductive medicine is pre-implantation genetic diagnosis (PGD). Through PGD, doctors and patients can learn about the genetic content of an embryo BEFORE it is implanted into the uterus. This information includes the number of chromosomes an embryo contains (normal is 46), the gender of the embryo and in some cases, if the embryo is affected by a specific genetic disease (like cystic fibrosis). Ultimately, PGD can both help prevent genetic disease and improve success rates for IVF.
To perform PGD, several general steps are required.
1. Embryos are created through in vitro fertilization (IVF)
2. The embryos grow in the IVF laboratory for 3 to 5 days
3. A precise biopsy procedure is used to remove a/some cell(s) from the embryo
4. The removed cells are transported to a DNA laboratory for analysis
5. The results of the DNA analysis are sent back to our IVF laboratory
6. Genetically healthy embryos are transferred into the uterus
The PGD biopsy can be performed anytime from the 3rd to the 5th day after an embryo is formed. The decision of which day to biopsy depends on several factors. Both day 3 and day 5 biopsy have their own advantages and disadvantages.
Day 3 biopsy
On the 3rd day after embryo formation, most embryos will be comprised of 8 cells (each cell is called a blastomere). A biopsy at this point, removes one of the 8 cells for analysis.
The biggest advantage of a day 3 biopsy is that the results will be available in time for the embryo to be freshly transferred into the uterus. This means that the embryo doesn’t need to be frozen while we wait for the results. This is advantageous because fresh embryo transfers have traditionally been thought to be more successful than frozen transfers (although this belief has recently come into question). Further, a fresh transfer is potentially less expensive than freezing the embryo and transferring it in the future. Lastly, a day 3 biopsy and transfer has the psychological advantage of not needing to wait a whole month until one can try to become pregnant.
The disadvantages of the day 3 biopsy stem from the the fact that only 1 cell can be biopsied (remember that the embryo is only comprised of 8 cells at this point). Thus, if there is a problem with that one cell, the results could theoretically inaccurately represent the rest of the embryo. Second, some people believe that a day 3 biopsy is more traumatic or damaging to the embryo than a day 5 biopsy.
Day 5 biopsy
On the 5th day after embryo formation, most embryos are comprised of more than 100 cells. A biopsy at this point includes the removal of 10 to 15 cells.
The advantage of a day 5 biopsy is that there is much more genetic material (from the 10-15 cells) which can be analyzed. This means that there is less theoretical chance for inaccurate or incomplete results when the DNA is analyzed. A second advantage is that the day 5 embryo is potentially more resilient to the biopsy than a day 3 embryo.
The biggest disadvantage of a day 5 biopsy is that it requires that the embryos are frozen. The reason for this is that an embryo must be transferred into the uterus by the fifth day after formation. Because of the technical nature of the DNA analysis, it usually takes a minimum of 24 hours to obtain the results. Thus, if the biopsy takes place on the 5th day, the results will not be available until the 6th day. The success rates of embryo transfer of the 6th day are significantly lower than the 5th. For this reason, we freeze the embryos on day 5 immediately after biopsy. The patient will then get her menses about 2 weeks later and then the embryo can be prepared to be transferred.
Ultimately, the decision between a day 3 and day 5 biopsy should be based on each patient’s individual situation and needs. If you have questions about embryo biopsy, PGD or any other reproductive medicine related questions feel free to contact us, we are happy to speak with you.